Outcome：

2023
Opto-thermal manipulation with 3 μm mid-infrared Er:ZBLAN fiber laser
Roukuya Mamuti, Masaya Shimizu, Takao Fuji, and Tetsuhiro Kudo
Optics Express 32 (7), 12160-12171 (2024)

2022
We performed opto-thermal trapping of colloidal particles with a 3μm　Er-doped ZBLAN fiber laser. We started from the laser generation of 3μm continuous laser. Water has a strong absorption at 3μm in wavelength due to the O-H vibrational mode. We achieved the trapping with much lower laser power compared to our previous study with the 2 μm laser.

2021
We performed opto-thermal trapping of polystyrene particles with a 2 μm Tm-doped fiber laser. By using the 2 μm　laser, water is directly heated and it enables the trapping of the particles along the temperature gradient.

Elucidate the behavior of viscous materials in spider webs.

Outcome：

2023
蜘蛛の巣の粘性物質の挙動解明のために高速スキャンレス広帯域中赤外ケミカルイメージングを行い、粘性物質が硬化する様子を明らかにした。

2022
A natural ionic liquid: low molecular mass compounds of aggregate glue droplets on spider orb webs
Yue Zhao, Takao Fuji, Masato Morita, andTetsuo Sakamoto
arXiv:2211.08818

Recently, non-contact electric field measurement methods using electric field-induced second harmonic generation have attracted much attention. Such non-contact electric field measurements are expected to expand to two-dimensional or three-dimensional electric field distribution measurements. This study successfully measured the two-dimensional electric field intensity and direction using an original imaging technique. We expect that this technique will provide a fast electric field distribution measurement technique for plasma engineering and various other scientific and industrial fields.

Outcome：

2022
Two-dimensional free space electric field imaging using electric field induced second harmonic generation
Yue Zhao and Takao Fuji
Optics Letters 47 (12), 2999-3002 (2022)

We have successfully generated extremely short mid-infrared light pulses using a unique technique called filamentation method [Opt. Express 28 36527 (2020)]. We are conducting research and development to further improve the generation technique in order to make the optical pulses available to a wide range of scientific and industrial fields.

Outcome：

2023
Sub-cycle mid-infrared pulse: generation and applications
Takao Fuji
Frontiers of ultrafast science: From fundamentals to applications
Invited talk

2022
繰り返し周波数を10kHzから5kHzに変更することで、中赤外光パルスが安定するようになった。この光源を利用して、これまでにない高速な赤外ハイパースペクトルイメージングを行うことができた。

2020
Generation of sub-half-cycle 10 µm pulses through filamentation at kilohertz repetition rates
Wei-Hong Huang, Yue Zhao, Shota Kusama, Fumitoshi Kumaki, Chih-Wei Luo, and Takao Fuji
Optics Express 28 (24), 36527-36543 (2020)

We are developing fast infrared spectroscopy and femtosecond pump-probe spectroscopy using 7-femtosecond mid-infrared light pulses generated by the filamentation method [J. Opt. 17 094004 (2015)].

Outcome：

2023
High-speed scanless entire bandwidth mid-infrared chemical imaging
Yue Zhao, Shota Kusama, Yuji Furutani, Wei-Hong Huang, Chih-Wei Luo, Takao Fuji
Nature Communications 14(1) 3929 (2023)

2022
サブサイクル中赤外光パルス光源の繰り返し周波数を10kHzから5kHzに変更することで、中赤外光パルスの強度が安定するようになった。この光源を利用して、これまでにない広帯域で高速な赤外ハイパースペクトルイメージングを行うことができた。

2020
Femtosecond time-evolution of mid-infrared spectral line shapes of Dirac fermions in topological insulators
Tien-Tien Yeh, Chien-Ming Tu, Wen-Hao Lin, Cheng-Maw Cheng, Wen-Yen Tzeng, Chen-Yu Chang, Hideto Shirai, Takao Fuji, Raman Sankar, Fang-Cheng Chou, Marin M. Gospodinov, Takayoshi Kobayashi, and Chih-Wei Luo
Scientific Reports 10, 9803 (2020)

Femtosecond pulsed laser oscillators and amplifiers using fluoride fiber as the laser medium, as well as solid-state laser amplifiers capable of generating even higher peak power pulses [Opt. Express 26 29460 (2018), Opt. Express 27 24499 (2019), Opt. Express 28 29918 (2020), Opt. Express 30 7332 (2022)].

Outcome：

2023
Dispersion-managed ultrafast laser based on thulium-doped ZBLAN fibers
Hiroki Kawase, Junya Takano, Takao Fuji
The 12th Asia-Pacific laser symposium

2022
Millijoule 265 fs Tm:YAP regenerative amplifier for driving ultrabroad band collinear mid-infrared optical parametric amplifiers
Seyed Ali Rezvani and Takao Fuji
Optics Express 30 (5), 7332-7339 (2022)

2020
Highly coherent multi-octave polarization-maintained supercontinuum generation solely based on ZBLAN fibers
Seyed Ali Rezvani, Kazuhiko Ogawa, and Takao Fuji
Optics Express 28 (20), 29918-29926 (2020)

2019
Generation and characterization of mid-infrared supercontinuum in polarization maintained ZBLAN fibers
S. A. Rezvani, Y. Nomura, K. Ogawa, and T. Fuji
Optics Express 27 (17), 24499-24511 (2019)

Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本光学会  

Language：English   Publishing type：Research paper (scientific journal)  

Water has significantly high absorption around 3 µm wavelength region, originated by its fundamental OH vibrational modes. Here, we successfully demonstrate an opto-thermal manipulation of particles utilizing a 3 µm mid-infrared Er:ZBLAN fiber laser (adjustable from 2700 to 2826 nm) that can efficiently elevate the temperature at a laser focus with a low laser power. The 3 µm laser indeed accelerates the formation of the particle assembly by simply irradiating the laser into water. By altering the laser wavelengths, the assembling speed and size, instantaneous particle velocity, particle distribution, trapping stiffness and temperature elevation are evaluated systematically. We propose that the dynamics of particle assembly can be understood through thermo-osmotic slip flows, taking into account the effects of volume heating within the focal cone and point heating at the focus.

DOI： 10.1364/OE.507935

Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.jpclett.3c01679

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Mid-infrared spectroscopy probes molecular vibrations to identify chemical species and functional groups. Therefore, mid-infrared hyperspectral imaging is one of the most powerful and promising candidates for chemical imaging using optical methods. Yet high-speed and entire bandwidth mid-infrared hyperspectral imaging has not been realized. Here we report a mid-infrared hyperspectral chemical imaging technique that uses chirped pulse upconversion of sub-cycle pulses at the image plane. This technique offers a lateral resolution of 15 µm, and the field of view is adjustable between 800 µm × 600 µm to 12 mm × 9 mm. The hyperspectral imaging produces a 640 × 480 pixel image in 8 s, which covers a spectral range of 640–3015 cm^–1, comprising 1069 wavelength points and offering a wavenumber resolution of 2.6–3.7 cm^–1. For discrete frequency mid-infrared imaging, the measurement speed reaches a frame rate of 5 kHz, the repetition rate of the laser. As a demonstration, we effectively identified and mapped different components in a microfluidic device, plant cell, and mouse embryo section. The great capacity and latent force of this technique in chemical imaging promise to be applied to many fields such as chemical analysis, biology, and medicine.

DOI： 10.1038/s41467-023-39628-6

Other Link： https://www.nature.com/articles/s41467-023-39628-6

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Optica publising group  

We have developed a chirped pulse amplification system for ultrashort 1300 nm pulses based on praseodymium-doped fluoride fibers (Pr:ZBLAN). The 1300 nm seed pulse is generated through soliton-dispersive wave coupling in a highly nonlinear fiber pumped by a pulse from an erbium-doped fiber laser. The seed pulse is stretched with a grating stretcher to ∼150 ps and amplified with a two-stage Pr:ZBLAN amplifier. The average power reaches ∼112 mW at the repetition rate of 40 MHz. The pulse is compressed to 225 fs by using a pair of gratings without serious phase distortion.

DOI： 10.1364/OE.485778

Other Link： https://opg.optica.org/viewmedia.cfm?URI=oe-31-10-16127&seq=0

Language：Japanese   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Optica Publishing Group  

An undulator is a device widely used in synchrotron light sources to produce a certain quasi-monochromatic light; however, its waveform has never been recorded due to the lack of measurement techniques. Here we propose an approach to characterize the waveforms of electric fields produced by relativistic electrons using an algorithm of spectral phase interferometry for direct electric-field reconstruction, which is one of the most common methods to characterize ultrashort laser pulses. As a result, we have succeeded in retrieving a 10-cycle square enveloped electric field, which corresponds to 10 periods of permanent magnets of the undulator. This method can dramatically improve the development of synchrotron sources including x-ray free electron lasers.

DOI： 10.1364/optica.477535

Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Optica Publishing Group  

Multiphoton microscopy has enabled us to image cellular dynamics in vivo. However, the excitation wavelength for imaging with commercially available lasers is mostly limited between 0.65–1.04 µm. Here we develop a femtosecond fiber laser system that produces ∼150 fs pulses at 1.8 µm. Our system starts from an erbium-doped silica fiber laser, and its wavelength is converted to 1.8 µm using a Raman shift fiber. The 1.8 µm pulses are amplified with a two-stage Tm:ZBLAN fiber amplifier. The final pulse energy is ∼1 µJ, sufficient for in vivo imaging. We successfully observe TurboFP635-expressing cortical neurons at a depth of 0.7 mm from the brain surface by three-photon excitation and Clover-expressing astrocytes at a depth of 0.15 mm by four-photon excitation.

DOI： 10.1364/boe.477322

Other Link： https://opg.optica.org/viewmedia.cfm?URI=boe-14-1-326&seq=0

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2644347

Authorship：Lead author   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1364/ASSL.2022.ATu4A.4

Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

Authorship：Lead author   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevapplied.18.054041

Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevApplied.18.054041/fulltext

Authorship：Last author   Publishing type：Research paper (international conference proceedings)   Publisher：OPTICA PUBLISHING GROUOP  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：OPTICA PUBLISHING GROUOP  

Authorship：Lead author,　Last author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Optica Publishing Group  

Generation of 265-fs millijoule pulses at 1940 nm from a solid-state regenerative amplifier has been demonstrated. The amplification chain consists of a thulium-doped fluoride (Tm:ZBLAN) fiber oscillator, a two stage Tm:ZBLAN fiber preamplifier, and a regenerative amplifier with a thermoelectrically cooled thulium-doped yttrium aluminium perovskite crystal. The newly developed light source is used for pumping an ultra broadband mid-infrared optical parametric amplifier based on a gallium selenide crystal. The 2.5–4 µm range of a multioctave supercontinuum, generated in a polarization-maintaining ZBALN fiber, is used as the MIR seed. The amplified signal in combination with the corresponding idler pulses spread from 2.5 to 10 µm in a collinear geometry.

DOI： 10.1364/oe.452429

Other Link： https://opg.optica.org/viewmedia.cfm?URI=oe-30-5-7332&seq=0

Publishing type：Research paper (scientific journal)   Publisher：The Optical Society  

DOI： 10.1364/oe.440866

Other Link： https://www.osapublishing.org/viewmedia.cfm?URI=oe-29-23-38314&seq=0

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人　レーザー学会  

Authorship：Last author   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/cleo/europe-eqec52157.2021.9541913

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Mid-infrared (MIR) light sources have much potential in the study of Dirac-fermions (DFs) in graphene and topological insulators (TIs) because they have a low photon energy. However, the topological surface state transitions (SSTs) in Dirac cones are veiled by the free carrier absorption (FCA) with same spectral line shape that is always seen in static MIR spectra. Therefore, it is difficult to distinguish the SST from the FCA, especially in TIs. Here, we disclose the abnormal MIR spectrum feature of transient reflectivity changes (ΔR/R) for the non-equilibrium states in TIs, and further distinguish FCA and spin-momentum locked SST using time-resolved and linearly polarized ultra-broadband MIR spectroscopy with no environmental perturbation. Although both effects produce similar features in the reflection spectra, they produce completely different variations in the ΔR/R to show their intrinsic ultrafast dynamics.

DOI： 10.1038/s41598-020-66720-4

Other Link： http://www.nature.com/articles/s41598-020-66720-4

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：The Optical Society  

DOI： 10.1364/oe.408342

Other Link： https://www.osapublishing.org/viewmedia.cfm?URI=oe-28-24-36527&seq=0

Authorship：Last author   Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)   Publisher：The Optical Society  

DOI： 10.1364/OE.404527

Publishing type：Research paper (scientific journal)   Publisher：Nature Research  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

An ultrafast, thulium-doped fiber laser system is developed for three-photon microscopy. The system generates 150 fs pulses at the center wavelength of 1.82 mu m with a pulse energy of 1.1 mu J at the repetition rate of 1 MHz. The generated pulses are applied to a three-photon fluorescence microscope, with which biological samples expressing red fluorescent proteins are observed through three-photon excitation processes. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

DOI： 10.1364/OSAC.395410

Authorship：Last author   Publishing type：Research paper (international conference proceedings)   Publisher：OSA  

DOI： 10.1364/assl.2020.jth6a.3

Authorship：Last author   Publishing type：Research paper (international conference proceedings)  

Authorship：Last author   Publishing type：Research paper (international conference proceedings)   Publisher：OSA  

DOI： 10.1364/up.2020.tu4b.5

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人　レーザー学会  

Authorship：Last author   Publishing type：Research paper (international conference proceedings)  

Authorship：Last author   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/app9163399

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1364/oe.27.024499

Authorship：Last author   Publishing type：Research paper (international conference proceedings)  

Publishing type：Research paper (scientific journal)   Publisher：EDP Sciences  

Carrier-envelope phase (CEP) controlled subcycle mid-infrared pulses from two-color laser filamentation have been applied for high harmonic (HH) generation in a crystalline silicon membrane. The HH spectrum reaches the ultraviolet region (<300 nm), beyond the direct band gap of the silicon. The shape of the HH spectrum shows the strong dependency on the CEP of the input pulse. The complete waveform characterization of the sub-cycle driver pulse with frequency-resolved optical gating capable of CEP determination is the effective method for the studies of the sub-cycle dynamics.

DOI： 10.1051/epjconf/201920502023

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：OSA - The Optical Society  

An ultrafast laser system at 1.8 µm is developed based on thulium-doped ZBLAN fibers. The generated pulses are used in a three-photon microscope to observe the images of fluorescent beads for ∼600 nm.

DOI： 10.1364/CLEO_SI.2019.SF2L.6

Authorship：Lead author,　Last author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

File： SSP54-693.PDF

Publishing type：Research paper (scientific journal)  

DOI： 10.1364/OE.26.029460

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OSA - The Optical Society  

Carrier-envelope-phase (CEP) controlled subcycle midinfrared pulses generated through two-color filamentation have been applied for high-harmonic (HH) generation in a crystalline silicon (Si) membrane. The HH spectrum reaches the ultraviolet region (&lt
300 nm), beyond the direct band gap of Si. The shape of the HH spectrum strongly depends on the CEP. The complex CEP dependence can be explained with the interference between different orders of the harmonics. The complete waveform characterization of the subcycle driver pulse using frequency-resolved optical gating capable of CEP determination plays a crucial role for investigation of the subcycle dynamics.

DOI： 10.1364/OL.43.002094

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

We have demonstrated high-harmonic generation (HHG) from a silicon thin crystal by using single-cycle mid-infrared pulses. The carrier-envelope phase dependence of the HHG spectrum was clearly observed.

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

We have demonstrated mid-infrared (MIR) sequential supercontinuum (SC) generation in fluoride and chalcogenide glass fibers pumped with a Thrium based master oscillator power amplifier. The spectrum of the SC reached up to 10μm.

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：OSA - The Optical Society  

We present a 2 GW peak power ring cavity diode-pumped Tm:YAP regenerative amplifier operating at 1 kHz repetition rate and centered at 1940 nm with 360 fs pulse duration.

DOI： 10.1364/ASSL.2018.AM5A.5

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

This paper is a perspective article which summarizes the development and application of sub-cycle mid-infrared (MIR) pulses generated through a laser filament. The generation scheme was published in Applied Sciences in 2013. The spectrum of the MIR pulse spreads from 2 to 50 mu m, corresponding to multiple octaves, and the pulse duration is 6.9 fs, namely, 0.63 times the period of the carrier wavelength, 3.3 mu m. The extremely broadband and highly coherent light source has potential for various applications. The light source has been applied for advanced ultrafast pump-probe spectroscopy by several research groups. As another application example, single-shot detection of absorption spectra in the entire MIR range by the use of chirped-pulse upconversion with a gas medium has been demonstrated. Although the measurement of the field oscillation of the sub-cycle MIR pulse was not trivial, the waveform of the sub-cycle pulse has been completely characterized with a newly developed method, frequency-resolved optical gating capable of carrier-envelope phase determination. A particular behavior of the spectral phase of the sub-cycle pulse has been revealed through the waveform characterization.

DOI： 10.3390/app7080857

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The wave nature of light has been known for more than 100 years. However, it is still very difficult to directly sample an optical field transient on a time scale below the oscillation period. It has been naturally believed that the field oscillation can be detected only by using a reference pulse that has a shorter duration than the period of the oscillation. In this Letter, an experimental demonstration of a self-referenced light wave measurement is shown. Frequency-resolved optical gating capable of carrier-envelope phase determination was used to measure the complete electric field evolution of a 21-fs few-cycle pulse without any reference pulses. A second harmonic generation frequency-resolved optical gating spectrogram and an interferogram between second harmonic and self-diffraction signals were simultaneously recorded. The phase-controlled light waves of few-cycle pulses were clearly observed by using this method.

DOI： 10.1002/lpor.201600244

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We demonstrate direct generation of sub-50 fs pulses doped fiber amplifier. Broad spectra are obtained by exploiting nonlinear effects within the amplifier fiber itself. High fractional inversion densities of thulium ions achieved by a core-pumping scheme helped to extend spectra into the shorter wavelength region around 1.7 mu m, Pulses with a duration of 48 fs are obtained at an average power of 2.5W directly after the amplifier fiber, i.e., without using a compressor. (C) 2017 Optical Society of America

DOI： 10.1364/OE.25.013691

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We demonstrate a chirped-pulse amplifier system operating around 1900nm using thulium-doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fibers. The pulses from a thulium-doped ZBLAN fiber laser oscillator are stretched by a passive ZBLAN fiber and subsequently amplified in a double-clad thulium-doped ZBLAN fiber to an average power of 6.9W at a pump power of 17W. We found that ZBLAN fibers require a much lower pump and/or seed power than silica fibers for efficient amplification. The amplified pulses are compressed to a duration of 150 fs with an average power of 3.9W. (C) 2017 The Japan Society of Applied Physics

File： APE10-012703.pdf

DOI： 10.7567/APEX.10.012703

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

In this study, we carried out 800-nm pump and ultra-broadband mid-infrared (MIR) probe spectroscopy with high time-resolution (70 fs) in bulk Ge. By fitting the time-resolved difference reflection spectra [Delta R(omega)/R(omega)] with the Drude model in the 200-5000 cm(-1) region, the time-dependent plasma frequency and scattering rate have been obtained. Through the calculation, we can further get the time-dependent photoexcited carrier concentration and carrier mobility. The Auger recombination essentially dominates the fast relaxation of photoexcited carriers within 100 ps followed by slow relaxation due to diffusion. Additionally, a novel oscillation feature is clearly found in time-resolved difference reflection spectra around 2000 cm(-1) especially for high pump fluence, which is the Lorentz oscillation lasting for about 20 ps due to the Coulomb force exerted just after the excitation.

File： SciRep7-40492.pdf

DOI： 10.1038/srep40492

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：OSA - The Optical Society  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Four-wave difference frequency generation (FWDFG) is a third-order optical parametric process, which is generally explained as omega(1) + omega(2) - omega(3) -> omega(4) or omega(1) - omega(2) - omega(3) -> omega(4), where three input frequencies are omega(1), omega(2), and omega(3), and the output frequency is omega(4). Here we report the use of FWDFG for chirped-pulse upconversion (CPU) of an ultrabroadband mid-infrared (MIR) supercontinuum and the application of the technique for MIR spectroscopy. When the CPU technique is used for MIR spectroscopy, ultrashort MIR pulses are converted into visible ones. This way, the spectra can be recorded with a visible spectrometer, which has much higher performance than MIR spectrometers. In the previous experiments, the CPU has been performed by using sum-frequency generation (SFG) with a solid crystal, and the bandwidth has been limited to less than 1000 cm(-1) due to the phase matching condition of the SFG. This limitation can be removed by using FWDFG, which is a third-order nonlinear process that allows us to use centrosymmetric nonlinear media such as gases for the upconversion. Since gaseous media have much less dispersion than solid media, the bandwidth of the phase-matching condition for the upconversion process becomes very broad. In our experiments, the entire spectrum of theMIR supercontinuum spanning from 200 to 5500 cm(-1) was upconverted by using a 4.9 ps chirped pulse to visible wavelength radiation, which was detected with a conventional visible dispersive spectrometer. The technique has been applied to attenuated total reflectance MIR spectroscopy. Absorption spectra of liquids in the range from 200 to 5500 cm(-1) were measured with a visible spectrometer on a single-shot basis.

File： JO17-094004.pdf

DOI： 10.1088/2040-8978/17/9/094004

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This paper summarizes the generation of sub-single-cycle infrared (IR) pulses through a laser filament and the detailed properties of the generated pulses. The fundamental (omega(1)) and second harmonic (omega(2)) of 30-fs Ti:sapphire amplifier output were focused into nitrogen gas and produced phase-stable broad-band IR pulses (omega(0)) by four-wave difference frequency generation (omega(1) + omega(1) - omega(2) -> omega(0)) through filamentation. The spectrum spread from 200 to 5500 cm(-1), corresponding to similar to 3.5 octaves. The waveform of the sub-single-cycle pulse was completely characterized with the frequency-resolved optical gating capable of a carrier-envelope phase determination. The pulse duration was measured as 6.9 fs, which was 0.63 times the period of the carrier frequency, 3000 cm(-1). The carrier-envelope phase of the IR pulse was passively stabilized, and the instability of the phase was estimated as 154-mrad rms over 2.5 h. We also summarize a particular behavior of the spectral phase of the sub-single-cycle pulse; the phase of high-frequency components of the generated pulses changes continuously and linearly with the relative phase between the two-color input pulses, whereas the phase of the low-frequency components takes only two discrete values. The phase behavior is a unique feature of single-cycle pulses generated with a passive carrier-envelope phase stabilization scheme.

File： JSTQE21-8700612.pdf

DOI： 10.1109/JSTQE.2015.2426415

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We demonstrate ultrabroadband and ultrafast midinfrared (MIR) pump-probe spectroscopy by employing the chirped-pulse up-conversion technique with four-wave difference-frequency generation in a gas. The full spectra of the MIR probe pulses, which spread from 200 to 5000 cm(-1), are recorded on a single-shot basis. We apply this MIR pump-probe spectroscopy to measure the ultrafast carrier dynamics of an intrinsic germanium crystal wafer. Ultrafast reflectivity change induced by the excitation of carriers is observed in the region from far to near infrared. The behavior of the reflectivity-change signals at each delay time is explained by the Drude model.

DOI： 10.1103/PhysRevApplied.3.051002

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：IEEE J. Sel  

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Carrier-envelope phase (CEP) of single-cycle pulses generated through two-color filamentation has been investigated. We have observed a particular behavior of the phase: the phase of high-frequency components of the generated pulses changes continuously and linearly with the relative phase between the two-color input pulses, whereas the phase of the low-frequency components takes only two discrete values. The transition of the phase behavior has been clearly observed by using frequency-resolved optical gating capable of CEP determination. We have found out that such a phase behavior is a unique feature of single-cycle pulses generated with a passive CEP stabilization scheme. (C) 2015 Optical Society of America

File： OL40-423.pdf

DOI： 10.1364/OL.40.000423

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Fluoride glass known as ZBLAN is well known for high transparency in the infrared region and is a promising candidate for the host material for infrared lasers. Furthermore, low material dispersion of ZBLAN glasses around 2-μm wavelength region suggests the usefulness of ZBLAN fibers for developing ultrafast fiber lasers. Based on these considerations, we have conducted a detailed study of ultrashort fiber laser oscillators based on thulium-doped ZBLAN fibers. Two types of diode-pumped, mode-locked oscillators are demonstrated using single-mode ZBLAN fibers and double-clad ZBLAN fibers. The oscillator with single-mode ZBLAN fibers generate stable output pulses at 67.5-MHz repetition rate with the average output power of 19 mW. The broad spectra spreading over 300 nm enabled the generation of pulses as short as 45 fs in 2-μm region. The oscillator with double-clad ZBLAN fibers was built with a multimode laser diode as the pump source and was successfully mode-locked at the pump power of 1.04 W. The output pulses with the spectrum extending over 150 nm are compressed to 90 fs.

DOI： 10.1109/JSTQE.2014.2325533

Authorship：Lead author   Publishing type：Research paper (scientific journal)  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：IEEE J  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Chirped-pulse upconversion technique has been applied to attenuated total reflectance (ATR) infrared spectroscopy. An extremely broadband infrared pulse was sent to an ATR diamond prism and the reflected pulse was converted to the visible by using four-wave mixing in krypton gas. Absorption spectra of liquids in the range from 200 to 5500 cm(-1) were measured with a visible spectrometer on a single-shot basis. The system was applied to observe the dynamics of exchanging process of two solvents, water and acetone, which give clear vibrational spectral contrast. We observed that the exchange was finished within similar to 10 ms. (C) 2014 Optical Society of America

File： OE22-29611.pdf

DOI： 10.1364/OE.22.029611

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Four-wave mixing (FWM) of femtosecond near-infrared laser pulses and its second harmonic in the filamentation regime is shown to give rise to ultrashort field waveforms in the mid-infrared with pulse widths as short as a half of the field cycle and produce ultrabroadband supercontinuum spectra stretching from the mid-IR to the terahertz region. Generation of 7-fs pulses centered at 4.35 mu m is demonstrated by a two-color filamentation experiment, where the 25-fs, 800-nm fundamental-wavelength output of a Ti: Sapphire laser is mixed with its second harmonic. The spectral and temporal properties of the mid-IR waveforms, as well as their emission pattern, are consistent with the FWM scenario of frequency conversion generalized to include the Kerr effect and ionization-induced refractive-index modulation.

File： APB117-611.pdf

DOI： 10.1007/s00340-014-5874-2

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We present real-time waveform characterization of ultrashort pulses by the use of a pulse-front tilt in frequency-resolved optical gating capable of carrier-envelope phase determination. Simultaneous measurement of cross-correlation frequency-resolved optical gating and electro-optic sampling signals has been realized without scanning any delays. Complete waveform characterization of single-cycle infrared pulses in real time has been demonstrated. The method has been also applied for characterization of more complex pulses, namely, a strongly chirped pulse after passing through a solid crystal or a distorted pulse due to the absorption of ambient air.

File： IEEEJP6-3300212.pdf

DOI： 10.1109/JPHOT.2014.2319091

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

An ultrafast, passively mode-locked fiber laser oscillator has been realized using thulium-doped ZBLAN fibers. Very low dispersion of ZBLAN glass fibers enabled generation of pulses with broad spectra extending from 1730 nm to 2050 nm. Pulses are obtained with the average power of 13mW at the repetition rate of 67.5MHz when the pump power is 140 mW. The output pulses are compressed with a pair of SF10 prisms and their durations are measured with SHG FROG, from which we obtained the pulse duration as short as 45 fs. (C) 2014 Optical Society of America

File： OE22-12461.pdf

DOI： 10.1364/OE.22.012461

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Recent progress of the coherent light synthesis technology has brought the generation of single-cycle pulses within our reach. To exploit the full potential of such a single-cycle pulse in any applications, it is highly important to obtain the full information of its electric field. Here we propose a novel pulse characterization scheme, which enables us to determine not only the intensity and phase profiles of ultrashort pulses but also their absolute carrier-envelope phase values. The method is based on a combination of frequency-resolved optical gating and electro-optic sampling, which can be extended to a self-referencing scheme to determine the electric field evolution of few-cycle ultrashort pulses. We have experimentally demonstrated the technique to characterize sub-single-cycle infrared pulses, and numerically studied the capability of the scheme to incorporate a self-referencing technique and to extend the wavelength range to visible region.

DOI： 10.1038/ncomms3820

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Single-shot detection of ultrabroadband mid-infrared spectra was demonstrated by using chirped-pulse upconversion technique with four-wave difference frequency generation in gases. Thanks to the low dispersion of the gas media, the bandwidth of the phase matching condition of the upconversion process becomes very broad and the entire mid-infrared spectrum spanning from 200 to 5500 cm(-1) was upconverted by using a 10 ps chirped pulse to visible wavelength radiation, which was detected with a conventional visible dispersive spectrometer. This method was demonstrated by the successful measurement of infrared absorption spectra of organic polymer films. (C) 2013 Optical Society of America

DOI： 10.1364/OE.21.018249

Language：English   Publishing type：Research paper (scientific journal)  

File： AS3-122.pdf

DOI： 10.3390/app3010122

Authorship：Last author   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Sub-single-cycle pulses in the mid-infrared (MIR) region were generated through a conical emission from a laser-induced filament. Fundamental and second-harmonic pulses of 25-fs Ti:sapphire amplifier output were focused into argon to produce phase-stable broadband MIR pulses in a well-focusable ring-shaped beam. The beam profile and spectrum of the MIR field are accurately reproduced with a simple calculation based on a four-wave mixing process. The ring-shaped pattern of the MIR beam originates from a dramatic confocal-parameter mismatch between the MIR field and the laser beams. (C) 2012 Optical Society of America

File： OE20-24741.pdf

DOI： 10.1364/OE.20.024741

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Ultrashort 198- and 158-nm pulses are generated simultaneously by cascaded four-wave mixing of the second and third harmonics of a 80-fs Ti:Sapphire laser in filamentation propagation through a single Ar gas cell. The energies of the 198- and 158-nm pulses are 7.6 mu J and 600 nJ, respectively. The duration of 198-nm pulse is determined to be ca. 45 fs by transient-grating frequency-resolved optical grating, which indicates that the pulse is intrinsically transform limited and chirped by the rear window of the gas cell. The spectral bandwidths of 198- and 158 nm support the transform limited pulse durations of 40 and 28 fs, respectively.

DOI： 10.1007/s00340-012-5146-y

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

The ultrafast dynamics of CS2 in the B-1(2)((1)Sigma(+)(u)) state was studied by photoelectron imaging with a time resolution of 22 fs. The photoelectron signal intensity exhibited clear vibrational quantum beats due to wave packet motion. The signal intensity decayed with a lifetime of about 400 fs. This decay was preceded by a lag of around 30 fs, which was considered to correspond to the time for a vibrational wave packet to propagate from the Franck-Condon region to the region where predissociation occurred. The photoelectron angular distribution remained constant when the pump-probe delay time was varied. Consequently, variation of the electronic character caused by the vibrational wave packet motion was not identified within the accuracy of our measurements.

DOI： 10.1002/asia.201100458

Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/1.3633259

Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/1.3586809

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Ultrafast photodynamics of furan has been studied by time-resolved photoelectron imaging (TRPEI) spectroscopy with an unprecedented time resolution of 22 fs. The simulation of the time-dependent photoelectron kinetic energy distribution (PKED) has been performed with ab initio nonadiabatic dynamics "on the fly" in the frame of time-dependent density functional theory. Based on the agreement between experimental and theoretical time-dependent photoelectron signal intensity as well as on PKED, precise time scales of ultrafast internal conversion from S(2) over S(1) to the ground state S(0) of furan have been revealed for the first time. Upon initial excitation of the S(2) state which has pi-pi* character, a nonadiabatic transition to the S(1) state occurs within 10 fs. Subsequent dynamics invokes the excitation of the C-O stretching and C-O-C out of plane vibrations which lead to the internal conversion to the ground state after 60 fs. Thus, we demonstrate that the TRPEI combined with high level nonadiabatic dynamics calculations provide fundamental insight into ultrafast photodynamics of chemically and biologically relevant chromophores. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3518441]

DOI： 10.1063/1.3518441

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We present experimental evidence of the generation of few-cycle propagating surface plasmon polariton wavepackets. These ultrashort plasmonic pulses comprised of only 2-3 field oscillations were characterized by an autocorrelation measurement based on electron photoemission. By exploiting plasmonic field enhancement, we achieved plasmon-induced tunnelling emission from the metal surface at low laser intensity, opening perspectives for strong-field experiments with low pulse energies. All-optical electron acceleration up to keV kinetic energy is also demonstrated in these surface-confined, few-cycle fields with only 1.35 x 10(12) W/cm(2) focused laser intensity. The experimental results are found to be in excellent agreement with the model. (C) 2010 Optical Society of America

DOI： 10.1364/OE.18.024206

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Transfer of spectral phase from near infrared ultrashort pulses to deep ultraviolet (UV) sub-30-fs pulses through four-wave mixing process is demonstrated. Micro joule UV pulses at 237 nm were generated by nonlinear mixing of second harmonic pulses of Ti:sapphire laser output and near infrared pulses from a noncollinear optical parametric amplifier. Chirp of the near infrared pulse was transfered to the UV pulse with the opposite sign. A positively chirped near infrared pulse was used for generating a negatively chirped UV pulse, which was compressed down to 25 fs by a magnesium fluoride window. (C) 2010 Optical Society of America

DOI： 10.1364/OE.18.016183

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

A nonadiabatic electronic transition through a conical intersection was studied by pump-probe photoelectron imaging spectroscopy with a 22 fs time resolution in the benchmark polyatomic molecule of pyrazine and deuterated pyrazine. The lifetimes of the S-2 state of pyrazine and deuterated pyrazine were determined to be 22 +/- 3 fs by the global fitting of the time-energy maps of photoelectron kinetic energy (PKE) distributions. The lifetime of S-3 was determined to be 40-43 fs. Two-dimensional maps of photoelectron distributions were obtained for time (t) and PKE, and individual PKE distributions upon ionization from S-2 and S-1 were extracted. Quantum beat with an approximately 50 fs period was observed after the S-2 -> S-1 internal conversion, which was attributed to the totally symmetric vibration nu(6a) in S-1. (c) 2010 American Institute of Physics. [doi: 10.1063/1.3395206]

File： JCP132-174302.pdf

DOI： 10.1063/1.3395206

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

A time-resolved photoelectron imaging using a femtosecond ultraviolet (UV) laser and a vacuum UV free-electron laser is presented. Ultrafast internal conversion and intersystem crossing in pyrazine in a supersonic molecular beam were clearly observed in the time profiles of photoioinzation intensity and time-dependent photoelectron images.

DOI： 10.1103/PhysRevA.81.031403

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Generation of ultrashort ultraviolet (uv) pulses by using nonlinear frequency conversion through filamentation was experimentally and theoretically investigated. By gently focusing second harmonic and fundamental Ti:sapphire laser pulses into gases, ultrashort uv pulses were efficiently generated by four-wave mixing processes through filamentation. The pressure dependence of the conversion efficiency cannot be explained by a one-dimensional model, but calculation of multicolor filament by a three-dimensional model was successful. The simulation result indicates a broad scalability of the scheme for frequency conversion of ultrashort pulses. The generated two-color uv pulses (200 and 260 nm) were successfully compressed down to similar to 15 fs.

DOI： 10.1103/PhysRevA.80.063822

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The ultrafast S(2) -> S(1) internal conversion of pyrazine through a conical intersection of the potential energy surfaces was clearly observed by ultrafast photoelectron imaging. The 2D time-energy map of the photoelectron angular anisotropy revealed a clear signature of the internal conversion (the color change of green-orange-green in the horizontal direction) at similar to 0.9 eV. The orange color at similar to 20 fs and 0.9 eV was found to correspond to the non-Koopmans ionization process from S(2)(pi,pi*) to D(0)(n(-1)).

DOI： 10.1021/ja904780b

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Laser Society of Japan  

Coherent soft x-ray radiation is generated by use of few-cycle mid-infrared (MIR) optical pulses around

DOI： 10.2184/lsj.37.271

Other Link： https://jlc.jst.go.jp/DN/JALC/00330374055?from=CiNii

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We produce carrier-envelope-phase-stable 15.7-fs (2-cycle) 740-mu J pulses at the 2.1-mu m carrier wavelength, from a three-stage optical parametric chirped-pulse amplifier system, pumped by an optically synchronized 49-ps 11-mJ Nd:YLF laser. A novel seed pulse spectral shaping method is used to ascertain the true amplified seed energy and the parametric superfluorescence levels. (C) 2008 Optical Society of America

DOI： 10.1364/OE.17.000062

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Generation of sub-two-cycle, microjoule pulses in the mid-infrared region is demonstrated. Fundamental and second-harmonic pulses of 25 fs Ti:sapphire amplifier output were focused into the air to produce extremely broadband mid-infrared pulses by four-wave difference-frequency generation through the filamentation. The full width at half-maximum of the spectral bandwidth reaches one octave (2.5 - 5.5 mu m), which is sufficiently broad for sub-single-cycle pulse generation. The pulse width was estimated to be 13 fs, without any compressors, by cross-correlation frequency resolved optical gating. The output energy of more than a few microjoule is sufficient for spectroscopy. (c) 2007 Optical Society of America.

DOI： 10.1364/OL.32.003330

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Generation of deep-ultraviolet femtosecond pulses by four-wave mixing through filamentation in neon gas was demonstrated. Fundamental (omega) and second-harmonic (2 omega) pulses of 25 fs Ti:sapphire amplifier output were focused into neon gas, and 20 mu J pulses with the center wavelength of 260 nm were produced by a four-wave mixing process, 2 omega+2 omega-omega ->omega through an similar to 15 cm filament. Additionally, pulses with an energy of 2 mu J at 200 nm were generated, probably by a cascaded process, 3 omega+2 omega-omega -> 4 omega. The 260 nm pulses were compressed by a grating-based compressor and characterized by a dispersion-free transient grating frequency-resolved optical gating. The estimated pulse width was 12 fs. (c) 2007 Optical Society of America.

DOI： 10.1364/OL.32.002481

Authorship：Last author   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

Photonic-crystal fibers are employed to demonstrate widely tunable frequency down-conversion of unamplified 6-fs Ti:sapphire laser pulses through the soliton self-frequency shift induced by the Raman effect. Wavelength shifts as large as 500 nm are achieved for input few-cycle pulses with broadband spectra centered at approximately 820 nm. The central wavelength of the redshifted output of a photonic-crystal fiber is smoothly tuned from the low-frequency edge in the spectrum of the 6-fs Ti:sapphire laser pulse up to 1.35 mu m by varying the input energy in the fundamental mode of the fiber.

DOI： 10.1103/PhysRevE.74.036617

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

The balance between diffraction and index-step guiding in photonic-crystal fibers is controlled by modifying the fiber structure, leading to different wavelength dependences of the effective mode area S-eff(lambda) and providing a mechanism to control nonlinear-optical phenomena. In optical fibers with a steep S-eff(lambda) profile, the guided mode of the light field tends to become much less compact with an increase in radiation wavelength, slowing down the Raman-induced soliton self-frequency shift of an ultrashort laser pulse. A 100-nm reduction of the soliton self-frequency shift is demonstrated for 6-fs input laser pulses.

DOI： 10.1103/PhysRevE.73.066617

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We demonstrate an optical parametric chirped-pulse amplifier producing infrared 20 fs (3-optical-cycle) pulses with a stable carrier-envelope phase. The amplifier is seeded with self-phase-stabilized pulses obtained by optical rectification of the output of an ultrabroadband Ti:sapphire oscillator. Energies of similar to 80 mu J with a well-suppressed background of parametric superfluorescence and up to 400 mu J with a superfluorescence background are obtained from a two-stage parametric amplifier based on periodically poled LiNbO3 and LiTaO3 crystals. The parametric amplifier is pumped by an optically synchronized 1 kHz, 30 ps, 1053 nm Nd:YLF amplifier seeded by the same Ti:sapphire oscillator. (c) 2006 Optical Society of America.

DOI： 10.1364/OL.31.001103

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We demonstrate direct simultaneous seeding of a few-cycle optical parametric chirped pulse amplifier (OPCPA) in the 700-1000-nm spectral range, and of a Nd:YLF amplifier emitting 30-ps pulses at 1053 nm by use of a chirped-mirror 6-fs Ti:sapphire oscillator. (1)This approach of employing a single master oscillator to drive two power amplifiers simplifies the pump laser design and is applied to eliminate the timing jitter between the seed and the pump pulses in the OPCPA chain. We show that 10 mJ fundamental picosecond pump pulses with the intensity contrast in excess of 10(4) relative to the nanosecond Q-switched background can be achieved with the seed intensity available in the edge of the oscillator spectrum around 1053 run. Cross-correlation measurements between the picosecond pump and femtosecond oscillator pulses reveal no traceable timing jitter between the OPCPA pump and seed pulses. The estimated long-term jitter of 0.3 ps is attributed to the thermal expansion of the cavity of the Nd:YLF regenerative amplifier.

DOI： 10.1109/JSTQE.2006.871930

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We demonstrate a novel scheme for carrier-envelope (CE) phase stabilization of few-cycle laser pulses from a mode-locked oscillator. Our scheme utilizes a monolithic, collinear geometry which obviates the need for splitting the laser output, where a fraction is used for CE-phase locking, in our scheme self-phase modulation and difference-frequency generation occur simultaneously in a single periodically poled lithium niobate (PPLN) crystal and are used to generate equivalent signals. Direct phase-locking and recompression of the output is enabled because the PPLN crystal transmits the majority of the incident fundamental relatively un-affected. As a result, the output provides few-cycle pulses with an unprecedented degree of short- and long-term reproducibility of the electric field waveform. These unique features, along with the simplicity of the scheme make it perfectly suitable for use in seeding CE-phase stabilized amplified laser systems. Results from 3 kHz amplified Ti:sapphire system will be presented that validate out assertions.

DOI： 10.1002/lapl.200510053

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Dispersive optical interference coatings (chirped mirrors - CMs) are designed by computer optimization of an analytically calculated initial multilayer. Traditionally, the relevant properties of the CM (reflectance and the frequency-dependence of the phase shift upon reflection) are optimized to match frequency-domain targets. We propose a novel target function that quantifies directly the capability of a multilayer to control the temporal shape of the reflected optical pulse. Employing this time-domain analysis/optimization one can design dispersive multilayers having air as medium of incidence and supporting the generation of pulses with durations in the sub-5-fs-range, as demonstrated in a proof-of-principle compression experiment. (c) 2005 Optical Society of America.

DOI： 10.1364/OPEX.13.010888

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

Photonic-crystal fibers with special dispersion profiles are shown to provide a high efficiency of spectral transformation of chirped sub-6-fs Ti:sapphire laser pulses. With the wavelength of zero group-velocity dispersion of the fiber lying within the broad spectrum of the input few-cycle pulse, the output spectra feature well-resolved spectral peaks, indicative of soliton self-frequency shift, four-wave mixing, and Cherenkov emission of dispersive waves. We demonstrate that up to 3% of radiation energy at the output of the fiber can be confined within a spectrally isolated soliton peak centered at 1060 nm, which is ideally suited as a seed for Nd:YAG- and ytterbium-based laser devices.

DOI： 10.1103/PhysRevE.72.056603

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

At present most laser systems for generating phase-stabilized high-energy pulses are chirped pulse amplifier systems that involve the selection and subsequent amplification of pulses from a phase-stabilized seed oscillator. We investigate the effect of the picking process on the carrier envelope phase stability and how the phase noise of the picked pulse sequence can be estimated from the phase noise properties of the seed oscillator. All noise components from the original pulse train above the picking frequency are aliased into the picked pulse train and therefore cannot be neglected. (c) 2005 Optical Society of America.

DOI： 10.1364/OL.30.002487

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Raman soliton phenomena in photonic crystal fibers are shown to allow efficient tunable frequency shifting of sub-10-fs laser pulses. Soliton self-frequency shift in a photonic-crystal fiber with a core diameter less than 2 mu m is used to transform the spectrum of a 6-fs 2-nJ Ti: sapphire-laser pulse, dominated by a 670-nm peak, into a spectrum featuring a well-resolved intense spectral component centered at 1064 nm, which is ideally suited as a seed for Nd: YAG- and ytterbium-based laser devices.

DOI： 10.1007/s00340-005-1929-8

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We demonstrate a significant simplification of the scheme for few-cycle Optical Parametric Chirped Pulse Amplification (OPCPA) which results in the elimination of a picosecond master oscillator and electronic synchronization loops. A fraction of a broadband seed pulse centered at 760 nm from a 70-MHz Ti: sapphire oscillator was frequency-shifted in a photonic crystal fiber to enable synchronized seeding of a picosecond Nd:YAG pump laser. The seed radiation at 1064 nm is produced in the soliton regime which makes it inherently more intense and stable in comparison with other methods of frequency conversion. The remaining fraction of the Ti: sapphire output is amplified with a FWHM bandwidth of 250 nm in a single timing-jitter-free OPCPA stage. Our work opens up the exciting possibility to use sub-picosecond pump pulses from highly efficient Yb-based amplifiers for jitter-less parametric amplification of carrier-envelope phase stabilized pulses from Ti: sapphire oscillators. (c) 2005 Optical Society of America.

DOI： 10.1364/OPEX.13.006550

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CAMBRIDGE UNIV PRESS  

This paper reports on a novel approach for producing high energy femtosecond pulses without external amplification. The so-called chirped-pulse oscillator (CPO) concept is based on an extended-cavity oscillator, operating at small net positive intracavity group delay dispersion (GDD), over a broad spectral range by the use of chirped multilayer mirrors. The resultant chirped picosecond pulses are compressed by a dispersive delay line external to the laser cavity. Utilizing this technique, sub-30 fs pulses with an energy exceeding 200 nJ at a repetition rate of 11 MHz were produced. The demonstrated peak power in excess of 5 MW is the highest ever achieved from a cw-pumped laser and is expected to be scaleable to tens of megawatts by increasing the pump power and/or decreasing the repetition rate. The demonstrated source allows micromachining of any materials under relaxed focusing conditions.

DOI： 10.1017/S0263034605050196

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

A new, monolithic scheme for stabilizing the phase between the carrier wave and the envelope (CE phase) in a train of few-cycle laser pulses is demonstrated. Self-phase modulation and second-harmonic generation or difference-frequency generation in a single periodically poled lithium niobate crystal, that transmits the main laser beam, allows for the CE-phase locking directly in the usable output. The monolithic scheme obviates the need for splitting off a fraction of the laser output for CE-phase control, coupling into microstructured fibre, as well as separation and recombination of spectral components. As a result, the CE-phase error integrated over the spectral range of 0.2 mHz-35 MHz is as small as 0.016 x 2 pi rad. This implies that the phase of the field oscillations (lambda similar to 830 nm) with respect to the pulse peak is locked to within 44 attoseconds, resulting in optical waveform control with subhundred attosecond fidelity for the first time.

DOI： 10.1088/1367-2630/7/1/116

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

The concept of optical parametric chirped-pulse amplification is applied to attain pulses with energies up to 8 mJ and a bandwidth of more than 100 THz. Stretched broadband seed pulses from a Ti:sapphire oscillator are amplified in a multistage noncollinear type I phase-matched beta-barium. borate parametric amplifier by use of an independent picosecond laser with lock-to-clock repetition rate synchronization. Partial compression of amplified pulses is demonstrated down to a 10-fs duration with a down-chirped pulse stretcher and a nearly lossless compressor comprising bulk material and positive-dispersion chirped mirrors. (C) 2005 Optical Society of America.

DOI： 10.1364/OL.30.000567

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

A new scheme for stabilizing the carrier-envelope (CE) phase of a few-cycle laser pulse train is demonstrated. Self-phase modulation and difference-frequency generation in a single periodically poled lithium niobate crystal that transmits the main laser beam allows CE phase locking directly in the usable output. The monolithic scheme obviates the need for splitting off a fraction of the laser output for CE phase control, coupling into microstructured fiber, and separation and recombination of spectral components. As a consequence, the output yields 6-fs, 800-nm pulses with an unprecedented degree of short- and long-term reproducibility of the electric field waveform. (C) 2005 Optical Society of America.

DOI： 10.1364/OL.30.000332

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Changing the chirp property of ultrashort pulses, the spectra of intensity and phase of the pulses after transmitting through ethanol solution of cyanine dye were measured with second-harmonic-generation frequency-resolved optical gating (SHG-FROG) method. Anomalous dispersion due to the absorption of the dye solution was not observed when the pulses were negatively chirped and their intensity were large. This phenomenon is well explained by suppression of the absorption by pump-dump process based on wave packet motion along the shifted harmonic potential model. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2004.09.128

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Highly sensitive dynamics of molecular vibration in a cyanine dye, 1,1',3,3,3',3'-hexamethyl-4,4',5,5'-dibenzo-2,2'-indotricarbocyanine (HDITC), was studied by path-length modulation pump-probe spectroscopy using 20 fs pulses. The observed real-time spectroscopic signal was decomposed into seven vibrational modes with well-determined phases by the singular-value decomposition method. Dependence of the vibrational phases for these modes on the probe wavelength was analyzed by the effective linear response function method. A significant change observed in this dependence by the relation between the excitation pulse duration and the mode frequency is discussed in terms of the wavepacket formation scheme. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2004.07.039

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We demonstrate a Kerr-lens mode-locked Ti:sapphire oscillator that generates 130-nJ, 26-fs and 220-nJ, 30-fs pulses at a repetition rate of 11 MHz. The generation of stable broadband, high-energy pulses from an extended-cavity oscillator is achieved by the use of chirped multilayer mirrors to produce a small net positive dispersion over a broad spectral range. The resultant chirped picosecond pulses are compressed by a dispersive delay line that is external to the laser cavity. The demonstrated peak powers, in excess of 5 MW, are to our knowledge the highest ever achieved from a cw-pumped laser and are expected to be scalable to tens of megawatts by an increase in the pump power and (or) a decrease in the repetition rate. The demonstrated source permits micromachining of any materials under relaxed focusing conditions. (C) 2004 Optical Society of America.

DOI： 10.1364/OL.29.001366

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Self-stabilized carrier-envelope offset phase is achieved by use of difference-frequency (DF) generation. The spectrum from a Ti:sapphire oscillator is broadened in a photonic crystal fiber, and a DF (900 nm) between the blue component (490 nm) and the infrared component (1080 nm) is generated. The beat signal between the fundamental and the DF signal is clearly observed. The wavelength of the DF signal can be tuned down to 780 nm, and hence the signal can be used for injection seeding of a Ti:sapphire oscillator. (C) 2004 Optical Society of America.

DOI： 10.1364/OL.29.000632

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We report on the generation of sub-30fs pulses from a mirror-dispersion-controlled (MDC) Ti:sapphire oscillator, containing a multiple-pass Herriott-cell for increasing the cavity length. Using that scheme, repetition rates down to some few MHz could be achieved. To avoid multiple pulsing instabilities, we operate the laser in a regime of slight positive group-delay dispersion (GDD) over a very broad wavelength range. This results in the formation of strongly chirped light pulses,, reducing the otherwise very high peak-intensity inside the laser crystal, which would limit the maximum output energy. We have investigated the spectral phase associated with these pulses with the help of the well known SPIDER-technique, and, based on the results, have constructed an optimized compressor.
When pumped with the full 10 W of a frequency-doubled Nd:YVO4 laser (Coherent Verdi V10), output energies well above 200 nJ could be obtained. As no signs of instabilities were observed, we believe, that our approach is scaleable to even higher energies if more powerful pump lasers are used.
Thanks to the excellent beam profile, high-resolution micromachining of various materials, including transparent dielectrica could be demonstrated.
Results on sub-micrometer surface modification of transparent materials will be presented.

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Vibrational coherence after internal conversion from the higher-lying excited singlet state to the first excited singlet state (S-n - S-i) and vibrational relaxation in cyanine dye molecules in solution are real-time observed with two-color pump-probe experiments with 20-fs time resolution. The intensity of oscillating signal due to 300-cm(-1) molecular vibration increases with time constant of about 1 ps. This phenomenon shows that the vibrational coherence preserves even after a large energy loss, 1.55 eV, by internal conversion and vibrational relaxation. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2003.08.057

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER-VERLAG  

We show with sub-20 fs pulses both experimentally and theoretically two techniques to control the width and polarization of spectral supercontinua generated in photonic crystal fibers. The first exploits double pulses which interact inside the fiber nonelastically due to stimulated Raman scattering and thus make the supercontinuum wider, whereas the peak intensity can be kept at a reasonably moderate level to prevent fiber damage. The second approach includes polarization manipulations which allow a desirable polarization state to be obtained in a definite spectral range and the spectral shape and width to be varied.

DOI： 10.1007/s00340-003-1187-6

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER-VERLAG  

Ultra-broad and smooth spectra are generated directly from a mirror-dispersion-controlled Kerr-lens mode-locked Ti:sapphire oscillator. The full width at half maximum of the spectrum is 277 nm. The pulse width is evaluated as 6.5 fs by using both interferometric autocorrelation and spectral phase interferometry for electric-field reconstruction. This compact, user-friendly source opens the door to routine implementation of ultra-high-resolution as well as spectroscopic optical coherence tomography in a clinical environment.

DOI： 10.1007/s00340-003-1254-z

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

DOI： 10.1364/OL.27.002046

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We demonstrate a scheme for parametric amplification that allows us to measure the drift of the carrier-envelope phase of the output signal pulses. The method is based on the unique double phase-matching properties of a noncollinearly pumped BBO crystal, making possible the detection of the interference between the signal and the frequency-doubled idler. Additionally, the suggested device greatly simplifies the single-shot measurement of the phase evolution in Ti:sapphire laser amplifiers by dispensing with harmonic synthesis from the spectral edges of an octave-wide supercontinuum. (C) 2002 Optical Society of America.

DOI： 10.1364/OL.27.001241

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

The phase link between signal, idler, and pump waves in a parametric interaction allows generation of an idler pulse with a phase independent of that of the input pulse. We suggest the use of a white-light seeded optical parametric amplifier as a self-stabilized source of few-cycle pulses, in which the phase of the electric field is exactly reproduced in each laser shot.

DOI： 10.1103/PhysRevLett.88.133901

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Angular dispersion of pump frequencies is shown to be an efficient mechanism for bandwidth enhancement in a noncollinear optical parametric amplifier. We demonstrate the generation of a continuous, simultaneously phase-matched 250-THz parametrically amplified spectrum. The resultant visible-near-IR signal-wave pulses were compressed to a 4-fs duration by a micromachined flexible mirror. Feedback for an iterative computer-controlled dispersion compensation algorithm is based on pulse characterization by second-harmonic generation frequency-resolved optical gating. (C) 2002 Optical Society of America.

DOI： 10.1364/OL.27.000306

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Transform-limited (TL) visible pulses with as short a duration as 4.7 fs with a 5 muJ pulse energy have been generated for the first time from a novel noncollinear optical parametric amplifier (NOPA). Applications of the sub-5-fs pulse source to the real-time spectroscopy of conjugated polymers, dye molecules, and J-aggregates are described. Several new phenomena, namely mode coupling, dynamic Duschinsky rotation, and dynamic intensity borrowing are found to take place in a polydiacetylene cast film, cresyl violet doped in polymers, and J-aggregates of porphyrin toluene sulfonate in aqueous solution.

Language：English   Publishing type：Research paper (international conference proceedings)  

Measurement and self-stabilization of carrier-envelope phase drift using an optical parametric amplifier (OPA) was presented. Self-stabilization was achieved in an OPA seeded with a white light that was derived from the pump pulse. The pulse-to-pulse fluctuation of CEP was inherited by white-light continuum pulse from the input laser pulse. Experimental results of the shot-to-shot CEP drift measurement indicated that spectra of frequency-doubled idler and signal waves, and mean intensity of the interference averaged over 300 laser shots. Precision of CEP pulse-to-pulse measurement was better than 0.1 rad.

Language：English   Publishing type：Research paper (international conference proceedings)  

Pathlength-modulation was used to distinguish between coherent and incoherent types of signals. By examining DTTCI molecules in ethanol, a clear insight into the vibrational wavepacket motion on the excited state was obtained. Data provide evidence of energy redistribution between two vibrational modes.

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Unusually intense overtones of three vibrational modes were found just after high-density excitation of phthalocyanine microcrystal film and they decay approximately with a power-law (t(2)) due to the Auger-type bi-excitonic quenching which induces anharmonic vibration. The decay is associated with vibrational relaxation in the lowest excited singlet state (exciton) after the internal conversion from a higher excited state (excited exciton). The observation of the high-frequency-overtone has become possible by feeding the higher vibrational levels by the Auger process, since small Franck-Condon factor do not allow population of the anharmonic vibrational levels by direct excitation. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-2313(01)00342-8

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Second-harmonic generation frequency-resolved optical gating and cross-correlation frequency-resolved optical gating were used as a characterization method of the phase and amplitude of pulses propagated through a 0.5-mm-thick plate of Nd3+-doped glass. Both experimental results of field intensity and phase were in fair agreement with the calculated result. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0030-4018(01)01510-3

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Transform-limited (TL) visible pulses with as short a duration as 4.7 fs with a 5-muJ pulse energy have been generated for the first time from a novel noncollinear optical parametric amplifier. Both signal-idler group-velocity matching and pulse-front matching are essential to generate coherent down-converted pulses compressible to the TL pulse with more than 150 THz bandwidth. Tunable operation with bandwidth-limited sub-10-fs pulses in the visible (550-700 nm) and near-infrared (900-1300 nm) ranges, achieved by increasing the seed chirp, is also a marked property. Applications for ultrafast spectroscopy of the sub-5-fs pulse source to the real-time spectroscopy of conjugated polymer, a dye molecule, and J-aggregates are also described.

DOI： 10.1109/2944.974223

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Excitation-induced modulation of vibrational frequency and amplitude in dye molecules was studied using sub-5-fs pulses. The frequency and amplitude modulations of the ring-breathing mode were clearly observed, indicating that the mode is coupled to another vibrational mode. The common modulated frequency and the depth of phase modulations were determined from the instantaneous frequency and amplitude. The two-dimensional (2D) potential surfaces were determined using a simple model of two-mode coupling. The anharmonicity appearing in the potential surfaces represents the Duschinsky effect. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0009-2614(00)01278-1

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

A new method for waveform measurement of photon echoes using a modified Michelson interferometer has been developed. The experimental setup uses collinear geometry, and photon echo signals are detected using a double-phase modulation technique. The amplitude and phase of photon echoes and those of excitation pulses are simultaneously measured by this technique. The method has been applied to a photon echo experiment on a dye solution. The results are explained using a stochastic modulation model with an accumulation effect of population grating.

DOI： 10.1143/JJAP.39.3429

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

Time-resolved phase sensitive pump-probe spectroscopy using a Michelson-type interferometer has been carried out. In this experiment, we obtain information on the time-resolved amplitude and phase of probe pulses by measuring cross-correlations between probe pulses and reference pulses. This method was demonstrated in an experiment on dye molecules, hexamethylin-dotricarbocyanine iodide, in ethylene glycol at room temperature. The experimental results indicated the time evolution of the phase and the increase in peak velocity of the probe pulse. These phenomena can be explained by phase velocity change and group velocity change due to thr pump pulse. A simulation based on a two-level Bloch model for the dye molecules reproduced the experimental results quite well.

DOI： 10.1143/JJAP.39.1738

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE  

The detailed dynamics of the vibration of the ring breathing mode in dye molecules, cresyl violet (CV), doped in a poly(vinyl alcohol) (PVA) film by using sub-5-fs pulses were studied. The evolution of the instantaneous frequency of the ring breathing mode was successfully taken into account. This was possible through analysis of the transient differential transmittance via calculation of spectrograms.

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN J APPLIED PHYSICS  

We observed the photonic band structure of one-dimensional photonic crystals using a white-light Michelson interferometer. fn one-dimensional photonic crystals with a structural defect, there is a localized mode where the field is localized around the position of the defect. If the defect is made of nonlinear optical material, the effective nonlinearity of the photonic crystal is largely enhanced by the enhanced light intensity at the defect. In a one-dimensional photonic crystal with a defect, we observed a large enhancement of degenerate four-wave mixing efficiency. Since the total thickness of the whole structure is only a few micrometers, it was successfully used to form an optical phase-conjugated image.

DOI： 10.1143/JJAP.38.6302

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

We used a Michelson-type interferometer to observe the waveform of the accumulated photon echoes in a 3,3'-diethylthiatricarbocyanine iodide-doped poly(vinyl alcohol) film. By Fourier analysis of the measured interferograms we obtained the shapes of the burned population grating and the phase grating in the sample. From the frequency distribution of the dye molecules, that is efficient for persistent spectral hole burning, we estimated the inhomogeneous frequency distribution of the 0-0 transition from S-0 to S-1 levels of the dye molecules in the poly(vinyl alcohol) film. (C) 1999 Optical Society of America [S0740-3224(99)00210-6].

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC JAPAN  

Linear propagation of two pulses through methanol solution of aluminum phthalocyanine chloride is investigated using a modified white-light Michelson interferometer. The observed coherence time of the white light is 6 fs, and the separation between the two-excitation pulses is set to about 10 fs. The excitation is dependent on the phase-relation between the two pulses. We have observed an enhancement of the excitation when the two pulses are in-phase and strong suppression of the excitation when the two pulses are out of phase by pi.

DOI： 10.1007/s10043-998-0263-x

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

A white-light Michelson interferometer in the visible and near infrared regions is described which can obtain the cross-correlation interferogram between the incident light and the transmitted light through samples or optical components. By comparing the autocorrelation interferogram of the incident white light with the cross-correlation interferogram between the incident light and the transmitted Light, we can obtain linear response functions of samples or optical components with femtosecond time resolution. Fourier analysis of the interferograms gives also the complex optical constants of the samples without relying on the Kramers-Kronig relation. (C) 1998 American Institute of Physics.

DOI： 10.1063/1.1149024

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MUNKSGAARD INT PUBL LTD  

A novel application of synchrotron radiation to ultrafast optical spectroscopy is demonstrated. The application is based on the short coherence time of broadband synchrotron radiation and employs a conventional interferometer. From a detailed study of the coherence of synchrotron radiation, it is shown that the coherent interference between two synchrotron radiation beams, split from a single beam, can provide ultimate time resolution down to a few femtoseconds. Experimental results of ultrafast spectroscopy using broadband synchrotron radiation are presented; these include free-induction decay and photon echoes in the visible and ultraviolet regions.

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Linear propagation of light was investigated by using a white-light Michelson interferometer. This method gives the full information on the deformation of broadband optical pulses by the passage through samples in the linear regime. We observed the delay of pulse propagation for cobalt chloride in pyridine, free-induction decay signal for oxazine 1 in methanol, and the increase of peak velocity for nigrosine in water. by Fourier analysis of the interferograms, complex optical constants of the samples were also obtained. (C) 1997 Optical Society of America.

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Femtosecond accumulated photon echoes excited by an incandescent lamp have been observed. To our knowledge, this is the first observation of photon echoes excited by incoherent black-body radiation where no stimulated emission takes place. This indicates that any kind of light source can be used to excite photon echoes, a kind of nonlinear coherent transient phenomena, if the intensity is large enough or the sample has a long enough accumulation time of population grating. The black-body radiation may facilitate the extension of the possible spectral range of the photon echo experiment.

DOI： 10.1016/0030-4018(96)00247-7

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Laser Society of Japan  

Ultrafast spectroscopy with a white-light Michelson interferometer is explained. By using anincandescent lamp, it is possible to obtain femtosecond time resolution both in the linear (freeinduction decay) and nonlinear (photon echo) spectroscopy.

DOI： 10.2184/lsj.23.954

Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Femtosecond free induction decay of cobalt-phthalocyanine in pyridine and of octaethyl porphine in pyridine was observed by use of a white-light interferometer with a resolution time of 6 fs. Also, frequency-domain complex optical constants of the samples were obtained by Fourier-transform analysis of the phase-sensitive interferograms.

Publishing type：Article, review, commentary, editorial, etc. (international conference proceedings)   Publisher：Optica Publishing Group  

Multi-octave spanning mid-infrared pulses are generated with a collinear optical parametric amplifier (OPA) based on a gallium selenide crystal. The OPA is pumped by femtosecond 2 μm pulses from a Tm:YAP regenerative amplifier.

DOI： 10.1364/up.2022.tu4a.38

Publishing type：Article, review, commentary, editorial, etc. (international conference proceedings)   Publisher：Optica Publishing Group  

Generation of 265-fs millijoule pulses at 1940 nm from a solid-state regen-erative amplifier has been demonstrated. The pulses have been used for pumping an ultrabroadband mid-infrared optical parametric amplifier.

DOI： 10.1364/mics.2022.mth5c.5

Authorship：Lead author   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：一般社団法人　レーザー学会  

Authorship：Last author   Publisher：IEEE  

DOI： 10.1109/cleo/europe-eqec52157.2021.9541913

Authorship：Lead author,　Last author,　Corresponding author   Publishing type：Article, review, commentary, editorial, etc. (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/cleo/europe-eqec52157.2021.9542558

Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publisher：IEEE  

DOI： 10.1109/pn52152.2021.9597908

Publisher：OSA  

We have experimentally demonstrated the generation of half-cycle pulses with the center wavelength of 10 µm through two-color filamentation in nitrogen with the duration of 12 fs, which corresponds to 0.36 cycles.

DOI： 10.1364/up.2020.tu4b.5

Publisher：OSA  

DOI： 10.1364/assl.2020.jth6a.3

Publisher：OSA  

DOI： 10.1364/mics.2020.mth3c.3

Authorship：Lead author   Publishing type：Article, review, commentary, editorial, etc. (other)   Publisher：株式会社　アグネ技術センター  

Publisher：OSA  

DOI： 10.1364/assl.2019.ath2a.4

Publisher：OSA  

DOI： 10.1364/assl.2019.ath2a.7

Language：English   Publisher：OSA - The Optical Society  

Carrier-envelope phase controlled sub-cycle mid-infrared pulses generated through two-color filamentation have been applied for high harmonic generation from crystalline silicon membrane. The high harmonic spectrum reaches the ultraviolet region.

DOI： 10.1364/CLEO_QELS.2018.FF2P.2

Language：English   Publisher：OSA - The Optical Society  

An ultrafast amplifier system operating in 2 μm region is developed using thulium-doped fibers. Spectral broadening within the amplifier fiber enabled generation of 50 fs pulses at an average power of 4.2W.

DOI： 10.1364/ASSL.2017.JTh2A.47

Language：English   Publisher：OSA - The Optical Society  

The electric field oscillations of few-cycle mid-infrared pulses were characterized by using a self-referencing technique based on frequency-resolved optical gating capable of carrier-envelope phase determination.

DOI： 10.1364/UP.2016.UTh2A.5

Language：English   Publisher：IEEE  

Self-referenced waveform characterization of ultrashort pulses has been experimentally realized. The electric field oscillations of few-cycle mid-infrared pulses were characterized without any reference pulses.

File： NCom4-2820.pdf

DOI： 10.1038/ncomms3820

Language：English   Publisher：IEEE  

We demonstrate a chirped-pulse amplifier system operating around 1900 nm using thulium-doped ZBLAN fibers. Pulses with a duration of 150 fs are obtained with average output power of 2.5 W.

Language：Japanese  

© Springer International Publishing Switzerland 2015.Mode-locked fiber laser oscillators are demonstrated by using thuliumdoped ZBLAN fibers. Thanks to very low dispersion of ZBLAN glass fibers, pulses as short as 45 fs are generated at 1,900 nm.

DOI： 10.1007/978-3-319-13242-6_179

Language：English   Publisher：SPRINGER-VERLAG BERLIN  

Carrier-envelope phase (CEP) of the single-cycle pulses generated through two-color filamentation has been investigated. It has been found that the phase of high frequency components of the generated pulses changes continuously and linearly with the relative phase between the two-color input pulses, whereas the phase of the low frequency components takes only two discrete values. To our knowledge, such behavior of the phase has never been discussed before. The transition of the phase behavior has been clearly observed by using frequency-resolved optical gating capable of CEP determination.

DOI： 10.1007/978-3-319-13242-6_176

Language：English   Publisher：IEEE  

Chirped-pulse upconversion technique has been applied to attenuated total reflectance infrared spectroscopy. The system was applied to observe the dynamics of exchanging process of buffers for biological tissues. (C) 2014 Optical Society of America

Language：English   Publisher：IEEE  

We demonstrated ultrabroadband mid-infrared pump-probe spectroscopy combined with chirped-pulse upconversion in a gas. Ultrafast reflectivity-change signal of an intrinsic germanium was observed in the region from 200 to 5000 cm(-1). (C) 2014 Optical Society of America

File： PRAp3-051002.pdf

DOI： 10.1103/PhysRevApplied.3.051002

Language：English   Publisher：SPRINGER-VERLAG BERLIN  

We have demonstrated infrared pump-probe spectroscopy using chirped-pulse upconversion with a nonlinear mixing in a gas. The ultrabroadband mid-infrared spectrum spanning from 200 to 5,000 cm(-1) was upconverted by using a 0.4 ps chirped pulse to visible wavelength generation in gas. This technique allow for the high speed and high sensitivity detection in ultrabroadband mid-infrared region. Ultrafast dynamics of free-carrier in Ge was clearly observed in the range 200-5,000 cm(-1).

DOI： 10.1007/978-3-319-13242-6_56

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We have demonstrated a new pulse characterization scheme, with which not only the intensity and spectral phase but also carrier-envelope phase can be measured. The scheme is based on a simultaneous measurement of electro-optic sampling and frequency-resolved optical gating (FROG) signals. A single-cycle infrared pulse has successfully been characterized with the scheme including carrier-envelope phase information. As is like FROG, various nonlinear interactions can be used with the scheme. Moreover, the scheme is capable for single-shot measurement and self-referencing. Such flexibility indicates broad application range of the new sheme.

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

We have demonstrated ultrabroadband mid-infrared pump-probe spectroscopy using chirped-pulse upconversion technique with a nonlinear mixing in a gas medium. Ultrafast pump-probe spectroscopy in a full mid-infrared region (200-5000 cm^<-1>) at high speed and high resolution has been realized with the technique. By using the system, we have measured ultrafast dynamics of phonon mode of Ge in the range of 200-5000 cm^<-1>.

© 2014 Optical Society of America.We have studied mode-locked operation of thulium-doped ZBLAN fiber laser oscillators around 2 μm wavelength region. Behavior of the output pulses from several different configurations are characterized.

Language：English   Publisher：IEEE  

We propose frequency-resolved optical gating capable of carrier-envelope phase determination using a reference pulse with a tilted pulse front. Real-time complete waveform measurement of ultrashort pulses has been demonstrated with the method. (C) 2014 Optical Society of America

Language：English   Publisher：IEEE  

We demonstrate a mode-locked fiber laser system using thulium-doped ZBLAN fibers. Very low dispersion of ZBLAN glass fibers enabled generation of pulses with the duration of 45 fs at 1900 nm. (C) 2014 Optical Society of America

Language：English   Publisher：ELECTROMAGNETICS ACAD  

We have demonstrated ultrabroadband infrared pump-probe spectroscopy using chirped pulse upconversion technique with a nonlinear mixing in a gas medium. Ultrafast pump-probe spectroscopy in a full mid-infrared region (200-5000 cm(-1)) at high speed has been realized with the technique. By using the system, we have measured ultrafast carrier dynamics in Ge in the range of 200-5000 cm(-1).

Language：English  

DOI： 10.1051/epjconf/20134111003

Language：English  

DOI： 10.1051/epjconf/20134112001

Language：English   Publisher：IEEE  

File： OE21-18249.pdf

DOI： 10.1364/OE.21.018249

Language：English   Publisher：IEEE  

Language：English   Publisher：IEEE  

Chirped-pulse upconversion of sub-single-cycle mid-infrared pulses with gaseous media has been realized. Single-shot detection of mid-infrared spectra from 250 to 5500 cm(-1) with 5 cm(-1) resolution was demonstrated. (C) 2013 Optical Society of America

Language：English  

Language：English   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Ultraviolet (UV) and vacuum-UV pulses (VUV) were simultaneously generated by using four-wave mixing through filamentation in neon gas. Second harmonic of Ti:sapphire laser output (400 nm, omega(SHG)) and near infrared pulses (1200 nm, omega(NIR)) from a noncollinear optical parametric amplifier were gently focused into neon gas, and ultrashort pulses with the center wavelengths of 237 nm (omega(fwm)) and 167 nm (omega(cas)) were produced by four-wave mixing processes omega(SHG) + omega(SHG) - omega(NIR) --&gt; omega(fwm) and omega(fwm) + omega(SHG) - omega(NIR) --&gt; omega(cas), respectively. The energy of the generated 237 nm pulse was more than one micro joule. Transfer of spectral phase from the near infrared ultrashort pulses to the UV pulses through the four-wave mixing process was also demonstrated. The even order spectral phase of the near infrared pulse was transfered to the UV pulse with the opposite sign, whereas the odd order spectral phase was transfered with the same sign. A positively chirped near infrared pulse was used for generating a negatively chirped UV pulse, which was compressed down to 25 fs by a magnesium fluoride window. In principle, the spectral phase transfer scheme can also be applied to the chirp control of the generated VUV pulses.

DOI： 10.1117/12.880921

Language：English  

Language：English  

Ultrafast internal conversion of pyrazine through a conical intersection was observed by photoelectron imaging with 22 fs time-resolution. The 2D time-energy map of the photoelectron angular anisotropy revealed a clear signature of the internal conversion. © OSA / UP 2010.

DOI： 10.1364/up.2010.thb6

Language：English  

Language：English   Publisher：IEEE  

Efficient frequency conversion of femtosecond optical pulses by four-wave mixing through filamentation is investigated in terms of experiment and theory The generated two-color deep-UV pulses were possible to use for time-resolved photoelectron imaging spectroscopy

Language：English  

DOI： 10.1109/CLEOE-EQEC.2009.5192587

Language：English  

DOI： 10.1109/CLEOE-EQEC.2009.5196384

Language：English   Publisher：SPRINGER-VERLAG BERLIN  

Generation of ultrashort pulses at 260 nm and 200 nm by four-wave mixing through filamentation in neon gas was demonstrated. Fundamental (omega(1)) and second-harmonic (omega(2)) pulses of 25 fs Ti:sapphire laser output were focused into neon gas, and 260 nm (omega(3)) pulses were produced by a four-wave mixing process, omega(2), + omega(2) - omega(1) -&gt;omega(3), through an similar to 15 cm filament. At the same time, 200 nm (omega(4)) pulses were also genereted by a cascaded process, omega(3) + omega(2) - omega(1) -&gt; omega(4), and/or by a sum frequency process, omega(2) + omega(1) + omega(1) -&gt; omega(4). The both pulses were simultaneously compressed by a grating-based compressor, and characterized by a trangient grating frequency-resolved optical gating. The estimated pulse widths of the 260 nm and 200 nm pulses were 14 Is and 16.5 fs, respectively.

Language：English  

We report the latest development of an OPCPA system, generating carrier-envelope-phase-stable 650-μJ 15-fs pulses around 2.1 μm. A novel seed-spectral-shaping method is used to resolve the non-trivial problem of ascertaining the true amplified signal energy. ©2008 IEEE.

DOI： 10.1109/LEOS.2008.4688741

Language：English   Publisher：IEEE  

Generation of mid-infrared pulses by four-wave mixing through filamentation in air has been demonstrated. The pulse width was measured as 13 fs, which corresponds to 1.3 optical cycles. The output energy reaches 1.5 mu J. (c) 2008 Optical Society of America

Language：English   Publisher：SPRINGER  

We demonstrate two types of all-optical synchronization of two lasers based on dissimilar gain materials, that significantly simplify the scheme for optical parametric chirped-pulse amplification (OPCPA). Both methods lead to negligible timing jitter between the OPCPA seed and pump and eliminate one master oscillator and all synchronization electronics. In the first approach, a fraction of a broadband Ti: sapphire seed oscillator centered at 760 nm is frequency shifted in a photonic crystal fiber to enable synchronized seeding of a picosecond Nd:YAG pump laser. The seed radiation at 1064 urn is produced in the soliton regime which makes it inherently more intense and stable in comparison with other methods of frequency conversion. In the second approach, we further simplify the setup by employing direct optical seeding of a Nd:YLF amplifier from the NIR wing of our Ti:sapphire oscillator. Our work opens up the exciting possibility to use sub-picosecond pump pulse from highly efficient Yb-based amplifiers for jitterless parametric amplification of carrier-envelope phase stabilized pulses from Ti:sapphire oscillators.

Language：English   Publisher：IEEE  

We report the latest progress on the development of a 1-kHz OPCPA system, generating carrier-envelope-phase-stabilized 350-mu J 20-fs pulses at 2.1 mu m with suppressed superfluorescence. A proof-of-principle high-harmonic generation experiment in argon was conducted. (C)2007 Optical Society of America

Language：English   Publisher：IEEE  

Generation of intense and broadband deep-ultraviolet pulses by four-wave mixing through filamentation in neon gas is demonstrated. The pulses are successfully compressed down to 13 fs by a grating-based compressor. (C) 2006 Optical Society of America

Language：English   Publisher：SPRINGER  

Language：English  

DOI： 10.1109/CLEOE-IQEC.2007.4386330

Language：English   Publisher：SPRINGER-VERLAG BERLIN  

We discuss routes towards developing an ultra-high peak power phase-stable source of few-cycle laser pulses suitable for driving a wide range of strong-field applications. Experiments with a phase-stable 0.1-TW 5-fs system based on a Ti:sapphire amplifier and the progress in construction of a 1-TW few-cycle optical parametric amplifier are presented.

Language：English   Publisher：OPTICAL SOC AMERICA  

A new scheme for stabilizing the carrier-envelope phase (CEP) of a few-cycle laser pulse train is demonstrated. Self-phase modulation and difference-frequency generation in a single periodically-poled crystal allows CEP locking directly in the usable output. (c) 2004 Optical Society of America.

Language：English   Publisher：OPTICAL SOC AMERICA  

We suggest and experimentally verify a simple method for timing-jitter-free synchronization of the seed and pump pulses in an optical parametric chirped-pulse amplifier. A fraction of a broadband seed pulse centered at 800 nm was frequency-shifted in a photonic crystal fiber to enable synchronized seeding of a picosecond Nd:YAG pump laser. (c) 2005 Optical Society of America.

Language：English   Publisher：SPRINGER-VERLAG BERLIN  

We report on the generation of ultra-broadband radiation utilizing the Chirped-pulse oscillator (CPO) concept. With this technique, pulse energies in excess of 150 nJ could be obtained directly out of a Kerr-lens-mode-locked Ti:sapphire oscillator. By spectral broadening of these pulses in a standard single-mode fiber, output spectra corresponding to a Fourier-limited pulse duration of 5,7 fs: at an energy of 50 nJ have been achieved. Due to the corresponding high peak intensity approaching 10 MW, direct measurement of the carrier-envelope phase of the pulses is feasible.

Language：English   Publisher：SPRINGER-VERLAG BERLIN  

The ultrafast dynamics of a cyanine dye is studied by the pump-probe spectroscopy using 20 fs pulses establishing a high sensitivity on the molecular vibration. The simulation reproduces the observed phase dependence on the mode frequencies.

Language：English   Publisher：Institute of Electrical and Electronics Engineers Inc.  

The paper discusses on the generation and full characterization of 4-fs phase-stabilized pulses as well as their temporal carrier-envelope phase (CEP) jitter, first experimental demonstration of a phase-sensitive detector on a base of photoemission effect from a solid target, and generation of a self-phase-stabilized signal based on a difference frequency generation.

DOI： 10.1109/LEOSST.2003.1224339

Language：English   Publishing type：Internal/External technical report, pre-print, etc.  

A pair of coherent femtosecond pulse excitations applied to a molecule with strong electron-phonon coupling creates a coherent superposition of a low-momentum and a high-momentum wavepacket in the vibrational states of both the excited state and the ground state of the coherent transition. As the excited state is accelerated further, interference between the high-momentum ground state contribution and the low-momentum excited state contribution causes a photon echo. This photon echo is a direct consequence of quantum interference between separate vibrational trajectories and can therefore provide experimental evidence of the non-classical properties of molecular vibrations.

DOI： 10.1088/1464-4266/4/2/303

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Language：English   Publisher：IEEE  

The use of a gradient index (GRIN) plate in a prism compressor is shown to more than triple the spectral range of the negative dispersion. We propose a design based on the use of novel photonic polymers, which provides a nearly linear group delay over 460-800 nm and is suitable for pulse compression down to 1.5 optical cycles.

Language：English   Publisher：IEEE  

A new, uniquely simple method for complete amplitude-phase characterization of broadband laser pulses is suggested and demonstrated experimentally. The spectral phase is determined from the fundamental and second-harmonic spectrogram of the interference between the test pulse an its chirped replica. The technique allows measuring pulses down to a single cycle in duration.

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：English   Publisher：OPTICAL SOC AMERICA  

Self-induced modulation of vibration in dye molecules doped in a polymer film was observed using sub-5-fs pulses. The modulation of potential curves was obtained from the frequency and amplitude modulations of the observed vibrational mode. (C) 2000 Optical Society of America OCIS codes: (320.0320) Ultrafast optics; (190.4710) Optical nonlinearities in organic materials.

Language：English   Publishing type：Internal/External technical report, pre-print, etc.   Publisher：OPTICAL SOC AMERICA  

Quantum interference between two distinct vibrational trajectories induced by two pulse femtosecond excitation in molecules is shown to result in a photon echo, providing direct evidence of the cat state superposition of Gaussian vibrational wavepackets, (C) 2000 Optical Society of America OCIS codes: (020.0020) Atomic and molecular physics;(270.0270) Quantum Optics; (020.1670) Coherent optical effects.

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Event date： 2024.8

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