尾松 孝茂

We demonstrated a widely tunable 1-mu m optical vortex laser formed from a 0.532-mu m optical vortex pumped optical parametric oscillator with a singly-resonant cavity configuration employing cascaded non-critical phase-matching LiB3O5 crystals. With this system, the topological charge of the pump beam can be selectively transferred to the signal or idler output, and a vortex output in the wavelength range of 850-990nmor 1130-1300nmcould be obtained. A maximum signal vortex output energy of 0.9 mJ was achieved, corresponding to an optical efficiency of 10%. (C) 2015 Optical Society of America

We present terahertz (THz) wave generation using type II phase matching polarization combination via difference frequency generation (DFG) with lithium niobate (LiNbO3) crystal. A collinear phase matching has not been realized so far because LiNbO3 crystal has a large absorption and high refractive index dispersion. In this paper we proposed that using type II phase matching is able to avoid these defects and generate the THz wave. We experimentally demonstrated the forward and backward collinear type II phase matching method, and confirmed that THz wave is generated by using simple equipment. This method will be applied for the applications for a small THz wave sources. (C) 2015 The Japan Society of Applied Physics

We demonstrated high average power, diffraction-limited (M-2 similar to 1.1) picosecond output from a sapphire face-cooled Nd:YVO4 slab amplifier at 1064 nm in a multi-pass geometry. Average output power of 44.5 W was achieved at an optical efficiency of 56%. A second harmonic power of 24.1 W was also obtained at an input fundamental power of 36 W, corresponding to a conversion efficiency of 67%. (C) 2015 Optical Society of America

A novel sensing technique is developed that makes use of evanescent terahertz (THz) waves without directly detecting the THz wave. The technique is demonstrated for measuring changes in the electric field of near-infrared light, transcribed from changes in the electric field of THz waves. The method will enable sensing of various materials in the THz-frequency region, to provide knowledge about chemical reactions that require real-time tracking.

We demonstrated widely tunable mid-infrared (6.3-12 mu m) optical vortex pulse generation from a ZGP difference frequency generator pumped by a 2 mu m optical vortex laser with a cascaded KTP geometry. The mid-infrared vortex output carried the same topological charge as that of the 1 mu m pump output without any destruction. A pulse energy of >135 mu J was obtained in the wavelength region of 6.3-7.0 mu m. (C) 2014 Optical Society of America

The frequency-doubling of a picosecond vortex fiber laser, formed of a 1-mu m picosecond master laser and a large-mode-area fiber amplifier by using a nonlinear LiB3O5, crystal, was performed. A maximum second-harmonic power of 7.7 W was achieved, corresponding to a conversion efficiency of 31 %. The second harmonic had an annular spatial form owing to a phase singularity with a doubled topological charge, and its wavefront helicity was selectively controlled by tuning the stress applied to the fiber amplifier.

This paper describes the first demonstration of ultraviolet (266nm) vortex generation using the combination of a frequency-doubled nanosecond green laser, a spiral phase plate, and a periodically bonded beta-BaB2O4 device. For a laser pumping energy of 9.1 mJ, an ultraviolet vortex energy of 1.24 mJ was obtained, corresponding to a conversion efficiency of 13.7%. (C) 2014 Optical Society of America

A terahertz (THz) spiral phase plate with high transmission (>90% after Fresnel correction) and low dispersion has been developed based on the Tsurupica olefin polymer. Direct observations of the topological charge (both magnitude and sign) of a THz vortex beam are performed by using a THz camera with tilted lens focusing and radial defect introduction. The vortex outputs with a topological charge of +/- 1 (or +/- 2) are obtained at a frequency of 2 (or 4) THz. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

We demonstrate intracavity frequency doubling of the selfRaman field generated within a diode end-pumped, solid state Nd: GdVO4 vortex laser. A maximum output power of 727 mW is generated at 586 nm with an overall diode-to-yellow conversion efficiency of 4%. Conservation of orbital angular momentum is observed under intracavity frequency doubling, with the topological charge of the yellow beam being twice that of the Stokes beam. (C) 2014 Optical Society of America

We report terahertz (THz) wave generation by satisfying Cherenkov phase-matching condition in both s and p polarizations. A dual-wavelength optical parametric oscillator is constructed from two potassium titanium oxide phosphate crystals pumped by a frequency-doubled Nd:YAG laser. By rotating the orientation of both a lithium niobate crystal (LiNbO3) and the polarization of the pump waves, the polarization of the THz wave changes. Due to the difference in the refractive index and absorption, the output power for p polarization is one tenth that for s polarization. A tuning range from 0.2 to 6.5 THz is obtained for s polarization, and from 0.2 to 4.2 and 5.4 to 6.9 THz for p polarization. The extraction efficiency is improved by changing the angle of prism for p polarization, and a large phase change occurs at total internal reflection. Consequently, p-polarized THz waves are optimal for spectroscopic applications. (C) 2014 Optical Society of America

We have discovered that a novel chiral structured surface relief (termed 'conch'-shaped surface relief) with a height of over 1 mu m can be formed in an azo-polymer film merely by employing circularly polarized optical vortex irradiation with a total angular momentum of j = +/- 2. The temporal evolution of the conch-shaped surface relief in the azo-polymer film was also observed. The results provide physical insight into how the angular momentum of light is transferred to a material through mass transport by cis-trans photo-isomerization. Such conch-shaped surface reliefs with chirality, in which functional chemical composites can be doped, enable new applications, such as planar chiral metamaterials, plasmonic holograms, and identification of chiral chemical composites.

We demonstrated broadband terahertz (THz) wave generation by satisfying the noncollinear phasematching condition with a reflected signal beam. We constructed a dual-wavelength optical parametric oscillator with two potassium titanium oxide phosphate crystals pumped by a frequency-doubled Nd:YAG laser. The collinear pump and signal waves were irradiated into a lithium niobate crystal. The pump and the signal waves were reflected at the crystal surface. Because the pump and the signal waves have a finite beam diameter, when the reflected signal wave and unreflected pump wave were irradiated at the correct angle, the noncollinear phase-matching condition was satisfied. By changing the incident angle to the crystal, broadband THz-wave generation with a range of over 0.2-7.2 THz was achieved. © 2013 Optical Society of America.

We present the first handedness control of an optical vortex output from a vortex-pumped optical parametric oscillator. The handedness of the optical vortex was identical to that of the pump vortex beam. Over 2 mJ, 2- μm optical vortex with a topological charge of ± 1 was achieved. We found that the handedness of a fractional vortex with a half integer topological charge can also be selectively controlled. © 2013 Optical Society of America.

We report a novel sensing technique that uses an evanescent terahertz (THz) wave, without detecting the THz wave directly. When a THz wave generated by Cherenkov phase matching via difference frequency generation undergoes total internal reflection, the evanescent THz wave is subject to a phase change and an amplitude decrease. The reflected THz wave, under the influence of the sample, interferes with the propagating THz wave and the changing electric field of the THz wave interacts with the electric field of the pump waves. We demonstrate a sensing technique for detecting changes in the electric field of near-infrared light, transcribed from changes in the electric field of a THz wave. © 2013 Optical Society of America.

We demonstrate the direct generation of a first-order LG(01) Laguerre Gaussian (vortex) mode operating at the first-Stokes wavelength of a diode end-pumped, Nd: GdVO4 self-Raman laser. To the best of our knowledge, this is the first report of intracavity stimulated Raman scattering (SRS) being used as a method for frequency conversion of a vortex laser beam and it is effective in enabling the frequency-converted (Stokes) beam to have the same LG(01) mode as the fundamental beam. (C) 2013 Optical Society of America

A high-average-power, high-beam-quality picosecond laser is presented that is based on CW diode side-pumped Nd:YVO4 thin-slab amplifiers having a bounce geometry. More than 65 W of output power with a beam quality of M-2 approximate to 1.3 is obtained at an optical-optical efficiency of 46%. (C) 2013 Optical Society of America

We discovered that chiral nanoneedles fabricated by vortex laser ablation can be used to visualize the helicity of an optical vortex. The orbital angular momentum of light determines the chirality of the nanoneedles, since it is transferred from the optical vortex to the metal. Only the spin angular momentum of the optical vortex can reinforce the helical structure of the created chiral nanoneedles. We also found that optical vortices with the same total angular momentum (defined as the sum of the orbital and spin angular momenta) are degenerate, and they generate nanoneedles with the same chirality and spiral frequency. DOI: 10.1103/PhysRevLett.110.143603

We obtained a frequency tunable, low-coherence, picosecond, terahertz (THz) output with a high repetition rate from a picosecond Nd:YVO4 bounce laser in combination with tandem periodically poled stoichiometric lithium tantalate and 4′-dimethylamino-N-methyl-4-stilbazolium tosylate crystals. The frequency of the THz output was tunable in the range 2.1-7.1 THz with a linewidth of ∼3.5 THz at 2.2 THz. The THz output had a maximum peak power of ∼180 mW and an average power of ∼0.65 μW at 3.9 THz. This system has the potential to realize ultra-high speed, THz coherence tomography. © 2013 Springer-Verlag Berlin Heidelberg.

A small forbidden gap matched to low-energy photons (meV) and a quasi-Dirac electron system are both definitive characteristics of bilayer graphene (GR) that has gained it considerable interest in realizing a broadly tunable sensor for application in the microwave region around gigahertz (GHz) and terahertz (THz) regimes. In this work, a systematic study is presented which explores the GHz/THz detection limit of both bilayer and single-layer graphene field-effect transistor (GR-FET) devices. Several major improvements to the wiring setup, insulation architecture, graphite source, and bolometric heating of the GR-FET sensor were made in order to extend microwave photoresponse past previous reports of 40 GHz and to further improve THz detection. © 2013 Mahjoub and Ochiai; licensee Springer.

We have rationally designed and synthesized a novel near-infrared (NIR) photoactivating probe, designated by iDOPE, in which an indocyanine green (ICG) fluorophore is covalently conjugated with a phospholipid moiety, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), to incorporate into liposome bilayers. NIR irradiation showed that iDOPE retained the optical and fluorescence properties of ICG and demonstrated photoactivator characteristics: fluorescence emission at around 820 nm in a solvent, singlet oxygen production, and concentration-dependent heat generation. Additionally, iDOPE was incorporated into liposome bilayers and maintained stable liposomally formulated iDOPE (LP-iDOPE) over 1 week under physiological conditions. We also observed the tumor-specific biodistribution of LP-iDOPE of in vivo xenografts. These findings suggest that LP-iDOPE might be a promising tool for NIR optical imaging, photodynamic therapy, and photothermal therapy. (C) 2012 Elsevier Ltd. All rights reserved.

We generated tunable 2-mu m optical vortex pulses with a topological charge of 1 or 2 in the wavelength range 1.953-2.158 mu m by realizing anisotropic transfer of the topological charge from the pump beam to the signal output in a vortex-pumped half-symmetric optical parametric oscillator. A maximum vortex output energy of 2.1 mJ was obtained at a pump energy of 22.8 mJ, which corresponds to a slope efficiency of 15%. The topological charges of the signal and idler output were investigated using a shearing interferometric technique employing a low-spatial-frequency transmission grating. (C) 2012 Optical Society of America

The highest power neodymium-doped mixed vanadate laser oscillator is presented. Using a crystal of Nd:Gd0.6Y0.4VO4 in the bounce geometry, average output powers of 27.5 W in multimode and 23 W in TEM00 operation were achieved. The first nonlinear mirror mode-locked operation of a mixed vanadate laser is also presented, with 16.8 W output power-the highest power mode-locked mixed vanadate oscillator, to the best of our knowledge. Self-starting continuous-wave mode locking was observed at a repetition rate of 100 MHz, pulse duration of 12.7 ps and central wavelength of 1063.8 nm, in TEM00 mode.

We have directly measured thermal lensing in a continuous-wave Nd-doped GdVO4 self-Raman laser under diode pumping at 808 and 879 nm. Thermal lensing increased significantly when generating first-Stokes emission, this most likely originating from impurity absorption and/or excited-state absorption at high pump powers. Pumping at 879 nm significantly reduced thermal lens effects in the laser crystal compared with pumping at 808 nm.

The thermal lens induced in an a-cut BaWO4 crystal by stimulated Raman scattering is measured using lateral shearing interferometry. The strength of the lens is proportional to the Stokes output power. For light polarized parallel to the a-axis, and a Stokes mode radius of 120 mu m, the lens is negative and highly astigmatic: -0.8 D W-1 in the plane parallel to the a-axis and -7.7 D W-1 in the plane parallel to the c-axis. The implications of this thermal lens for Raman laser design are discussed. (C) 2012 Optical Society of America

The current trends in stimulated Brillouin scattering and optical phase conjugation are overviewed. This report is formed by the selected papers presented in the "Fifth International Workshop on stimulated Brillouin scattering and phase conjugation 2010" in Japan. The nonlinear properties of phase conjugation based on stimulated Brillouin scattering and photorefraction can compensate phase distortions in the high power laser systems, and they will also open up potentially novel laser technologies, e. g., phase stabilization, beam combination, pulse compression, ultrafast pulse shaping, and arbitrary waveform generation.

We demonstrated MHz-repetition-rate, picosecond THz output from DAST crystal pumped by 1.5μm dual-frequency laser system based on picosecond Nd-doped vanadate bounce laser. THz output was observed in the frequency range of 2.1-7.1 THz. © 2012 OSA.

Dual-frequency MHz-repetition 1.5-mu m optical parametric generation is demonstrated from a tandem system pumped by a picosecond Nd:YVO4 bounce laser. An average power of 1.0 W is obtained over the range 1571-1630 nm, corresponding to an optical-optical conversion efficiency and slope efficiency of 16% and 23%, respectively. Terahertz-wave with a frequency of 3.2 THz is also generated from the system in combination with an organic nonlinear DAST crystal. (C) 2011 Optical Society of America

Nanosecond vortex pulses were generated using a stressed, large-mode-area, Yb-doped, fiber amplifier with an off-axis coupling technique for the first time. A pulse energy of 0.83 mJ (corresponding to a peak power of 59 kW) was achieved at a pump power of 25.7 W. The optical-optical efficiency was measured to be 31%. The millijoule nanosecond vortex pulses will be potentially applied to novel material processing, such as metal microneedle fabrication. (C)2011 Optical Society of America

The first demonstration of a mid-infrared optical parametric oscillator pumped by 1-mu m optical vortex pulses is presented. A 0.5-mJ 2-mu m fractional vortex pulse having half-integer topological charge is generated. Using this system, 0.24-mJ vortex pulses with a topological charge of 1 can be created. The topological charges of the mid-infrared vortex pulses are observed by an interferometric technique in combination with second-harmonic frequency conversion. (C) 2011 Optical Society of America

We investigated the properties of 4,4'-biphenyl dicarboxylic acid diethyl ester (PCE). The PCE underwent a 2-step reduction at -1.5 V and -2.2 V. The color of the PCE changed from colorless to yellow in the first step and consequently to red in the second reduction step. A PCE based EC cell using an NiO-modified electrode was also fabricated. The NiO electrode worked as a counter reaction material for PCE reduction. The PCE-NiO cell achieved multi-coloration ranging from colorless to yellow and red, and also achieved high coloration efficiency and long term switching stability.

Power scaling of a picosecond vortex laser based on a stressed Yb-doped fiber amplifier is analyzed. An output power of 25 W was obtained for 53 W of pumping, with a peak power of 37 kW. Frequency doubling of the vortex output was demonstrated using a nonlinear PPSLT crystal. A second-harmonic output power of up to 1.5 W was measured at a fundamental power of 11.2 W. (C) 2011 Optical Society of America

6.5-W, 1.3-A mu m passively Q-switched output was demonstrated from a side-pumped Nd-doped Gd(0.6)Y(0.4)VO(4) bounce laser in combination with a V:YAG saturable-absorber crystal. Experimental output powers of 6.5 W and 6 W were measured at a maximum pump level in multi- and TEM(00)-mode operations, corresponding to optical-to-optical efficiencies of 17.5% and 16.2%, respectively.

Microneedle fabrication on a metal surface based on laser ablation using twisted light with spin was demonstrated, for the first time. The resulting needle showed a height of at least 10 mu m above the target surface and a tip diameter of less than 0.3 mu m. We also demonstrated the fabrication of a two-dimensional 5 x 6 microneedle array. The needles were uniformly well shaped with an average length and tip diameter of about 10 and 0.5 mu m, respectively. (C) 2010 Optical Society of America

Laser ablation of Ta plates using nanosecond optical vortex pulses was carried out, for the first time. It was suggested that owing to orbital angular momentum of optical vortex, clearer and smoother processed surfaces were obtained with less ablation threshold fluence, in comparison with the ablation by a nonvortex annular beam modified from a spatially Gaussian beam. (C) 2010 Optical Society of America

We demonstrated MHz-repetitive mid-infrared generation from a PPSLT-OPG pumped by a pico-second Nd:YVO4 bounce laser system. Average power of 640mW was obtained in a frequency range of 1.58-1.63μm, corresponding to a slope efficiency of 18.2%. © 2010 Optical Society of America.

We scale the power of a pico-second vortex master-oscillator power amplifier system based on a stressed large-mode-area fiber amplifier. The vortex output power of &gt 20 W with the corresponding peak power of &gt 30kW was obtained. © 2010 Optical Society of America.

A 50W pico-second dual Nd:GdVO4 bounce amplifier system with a phase-conjugate mirror is demonstrated. The system has also been extended to generate pico-second mid-infrared radiation with frequency ranges of 1.55-1.57μm and 3.4-3.3 μm. © 2010 Optical Society of America.

We report, for the first time to our knowledge, on picosecond-pulse optical phase conjugation using photorefractive Sn2P2S6 crystals. For 7.2-ps pulses at 1.06 mu m, we have achieved phase-conjugate reflectivities of up to 45% with very fast build-up times, about 15 ms at an intensity of 23 W/cm(2) using Te-doped Sn2P2S6. We furthermore demonstrate aberration-free 5 W optical output of 8-ps pulses at 1.06 mu m from a side pumped Nd:YVO4 amplifier using the Sn2P2S6-based phase-conjugate feedback. (C) 2009 Optical Society of America

We have demonstrated a distributed-feedback plastic waveguide blue laser using Fluorescent Brightener 135 pumped by a picosecond pulse laser. The optical properties of Fluorescent Brightener 135 and its laser properties including photostability were investigated. The experimental laser slope efficiency and energy threshold were 8.2% and 24 mu J, respectively. An operation lifetime of 5,000 shots was attained under a pump pulse energy of 28 mJ at a wavelength of 355 nm. (C) 2010 The Japan Society of Applied Physics

Passively Q-switched yellow output from a frequency-doubled self-stimulating Raman composite Nd:YVO4/YVO4 laser using a Cr:YAG saturable absorber is reported. Maximum yellow output power of 264 mW was obtained with corresponding diode to yellow conversion efficiency of 5.9%.

High power passive Q-switching of a diode-side-pumped Nd:YAG ceramic bounce laser at 1.3 mu m is demonstrated. The laser operates from 18 to 114 kHz pulse repetition frequency, producing pulses of 55140 ns duration. Average output power of 5.8 W was obtained from 52 W of pump power. Five Watts of high beam quality output was also achieved in an asymmetric cavity geometry. (C) 2009 Elsevier B.V. All rights reserved.

We demonstrated > 80 W picosecond output at a pulse repetition frequency of 100 MHz from a dual Nd:YVO4 amplifier laser system consisting of a phase-conjugate Nd:YVO4 bounce amplifier combined with a second diode-side-pumped Nd:YVO4 bounce amplifier. The output exhibited high quality spatial form with M-2 < 1.8 and a pulse duration (FWHM) of 9.2 ps. A peak power of > 7.4 MW with an average power of 78.5 W was also achieved at a pulse repetition frequency of 1.0 MHz. (C) 2009 Optical Society of America

We have demonstrated a highly efficient, long-lifetime waveguide dye laser using nanosized-particle-dispersed random scattering active media An experimental laser slope efficiency of 38.6% and energy threshold of less than 1 mu J at a single longitudinal mode were measured The operation lifetime of this laser device reached 6.5 million pump shots (C) 2009 The Japan Society of Applied Physics

We present the production of picosecond vortex pulses from a stressed large-mode-area fiber amplifier for the first time. 8.5 W picosecond output with a peak power of similar to 12.5 kW was obtained at a pump power of 29 W. 2009 Optical Society of America (C) 2009 Optical Society of America

We directly produced for the first time a high-power 1.06 mu m vortex mode from a diode-pumped Nd:GdVO4 bounce amplifier. A maximum output of 17.8 W was achieved for a pump power of 55 W. The corresponding optical efficiency from the diode to the output was above 30%.

We demonstrate a high average power similar to 4 ps output from a phase conjugate laser system based on a diode-side-pumped Nd:Gd0.6Y0.4VO4 bounce amplifier. An average output power of 16.2 W with a peak power of 210 kW was achieved. A corresponding extraction efficiency of 23% was measured. (c) 2008 Optical Society of America

An overview on current trends in stimulated Brillouin scattering and optical phase conugation is given. This report is based on the results of the "Second International Workshop on stimulated Brillouin scattering and phase conjugation" held in Potsdam/Germany in September 2007. The properties of stimulated Brillouin scattering are presented for the compensation of phase distortions in combination with novel laser technology like ceramics materials but also for e.g., phase stabilization, beam combination, and slow light. Photorefractive nonlinear mirrors and resonant refractive index gratings are addressed as phase conjugating mirrors in addition.

We produced a high power radially-polarized output directly from a diode-pumped Nd:YVO4 bounce amplifier, using an autocloned photonic crystal mirror as an output coupler, with a simple cavity configuration. The radially-polarized output power of similar to 6 W was achieved, and a corresponding slope efficiency was estimated to be similar to 17 %. The output was characterized to be an ideal radially-polarized beam from its polarization distribution profiles. The output mode was not an eigenmode in the resonator. We discussed and clarified intra-cavity mode dynamics in terms of polarization distribution in the wavefront. (C) 2008 Optical Society of America.

High power passive Q-switching was achieved with a pulse width of 18-32 ns by using a diode-side-pumped Nd:Gd0.6Y0.4VO4 bounce amplifier. An average output power of > 8 W was obtained at a pump power of 39 W. The peak power of the Q-switched output was adjusted within 1.9-5.2 kW by changing the Nd concentration. The mixed vanadates showed significantly higher Q-switching performances in comparison with pure Nd:GdVO4.