宮本 克彦

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

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 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

We discovered for the first time that light can twist metal to control the chirality of metal nanostructures (hereafter, chiral metal nanoneedles). The helicity of optical vortices is transferred to the constituent elements of the irradiated material (mostly melted material), resulting in the formation of chiral metal nanoneedles. The chirality of these nanoneedles could be controlled by just changing the sign of the helicity of the optical vortex. The tip curvature of these chiral nanoneedles was measured to be <40 nm, which is less than 1/25th of the laser wavelength (1064 nm). Such chiral metal nanoneedles will enable us to selectively distinguish the chirality and optical activity of molecules and chemical composites on a nanoscale and they will provide chiral selectivity for nanoscale imaging systems (e.g., atomic force microscopes), chemical reactions on plasmonic nanostructures, and planar metamaterials.

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.

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 demonstrated 1.5 mu m dual-frequency optical parametric generation from tandem PPSLT crystals pumped by a pico-second Nd-doped vanadate bounce laser. The signal frequency was controlled in the range 1.57-1.63 mu m. A signal power of 1.54W was achieved. (C) 2010 Optical Society of America

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.

We achieved high-sensitivity, rapid-response detection of terahertz (THz) waves using an organic nonlinear optical crystal, 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST). Nonlinear up-conversion in the crystal resulted in a shift of THz waves to near-infrared radiation at room temperature. A minimum THz-wave peak power of about 300 mu W was measured at 19.2 THz by detecting the up-converted optical signal with an InGaAs-based photodetector. A noise equivalent power of about 6 nW/Hz(1/2) was estimated in this experiment. Optimum conditions were obtained for THz-wave detection using a DAST crystal. (C) 2010 American Institute of Physics. [doi:10.1063/1.3489097]

A method for simultaneously measuring the refractive index and absorption coefficient of nonlinear optical crystals in the ultra-wideband terahertz (THz) region is described. This method is based on the analysis of a collinear difference frequency generation (DFG) process using a tunable, dual-wavelength, optical parametric oscillator. The refractive index and the absorption coefficient in the organic nonlinear crystal DAST were experimentally determined in the frequency range 2.5-26.2 THz by measuring the THz-wave output using DFG. The resultant refractive index in the x-direction was similar to 2.3, while the absorption spectrum was in good agreement with FT-IR measurements. The output of the DAST-DFG THz-wave source was optimized to the phase-matching condition using the measured refractive index spectrum in THz region, which resulted in an improvement in the output power of up to a factor of nine. (C) 2010 Optical Society of America

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

Ultrabroadband terahertz generation up to 200 THz has been demonstrated using a 5 fs Ti:sapphire laser and a 4-N,N-dimethylamino-4(&apos;)-N(&apos;)-methyl-stilbazolium tosylate (DAST) crystal. The high-frequency components beyond 100 THz are much stronger than those generated using conventional electro-optic crystals such as GaSe. A simple simulation of the difference frequency generation in the DAST crystal by considering the refractive index dispersion can reproduce the broadband generation of the terahertz wave and its chirp dependence. Because the generated terahertz wave is coherent and has a broad bandwidth, it can serve as a suitable light source for ultrabroadband terahertz time-domain spectroscopy of a material. (C) 2010 American Institute of Physics. [doi:10.1063/1.3463452]

Optical trapping and manipulation of Au submicron-particles using a holographic tweezer (multiple vortex tweezer) based on optical multiple vortex involving several phase singularities in a wavefront was presented.

We demonstrated &gt; 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 &lt; 1.8 and a pulse duration (FWHM) of 9.2 ps. A peak power of &gt; 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

An effective and widely tunable means of producing terahertz (THz) radiation using difference-frequency generation (DFG) in an organic N-benzyl-2-methyl-4-nitroaniline (BNA) crystal was demonstrated by optimizing the pump wavelengths. We calculated the (wideband) refractive index and coherence length mapping of BNA to establish the optimum phase-matching condition of the DFG configuration. To satisfy the phase-matching conditions over the range 0.1-20 THz, both pump wavelengths were varied from 780 to 950 nm, and the optical wavelength dependency of the THz-wave output was clearly observed. We expanded the range of THz-wave generation and increased the power output to ten times that obtained using previous methods. (C) 2009 Optical Society of America

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 developed a method for mapping the carrier density on a semiconductor substrate surface based on terahertz (THz)-reflective measurement. Reflectivity in the THz-frequency region away from the optical phonon frequency is sensitive to the carrier density in semiconductors. However, reflectivity in the optical phonon frequency regions is around 1.0, independent of the carrier density. We developed a THz-reflective spectral imaging system using a frequency-agile, ultra-widely tunable THz source (1-40 THz). Different reflective images were obtained from GaN samples of carrier density 2.5 x 10(16) cm(-3), 1.0 x 10(18) cm(-3) and 1.5 x 10(18) cm(-3) using 22.7 and 26.5 THz. The image contrast reflected the GaN crystals&apos; carrier density. [DOI: 10.2971/jeos.2009.09012]

We studied the solidification and inelting of certain complex scattering substances by laser Raman spectroscopy. We used a modified laser Raman system to study the spectrum of certain long-chain organic substances (paraffin and candlewax) during solidification and melting, and found that there is a significant and discontinuous change in linewidth (by 4-5 times) during these processes. By measuring the linewidth of a certain line during solidification, we show that at a microscopic level, there is a large change in the immediate microscopic environment and damping, of the molecular motions. This shows that Raman spectroscopy can be used Lis a sensitive probe of the change in the immediate environment of the molecular motions in these systems. [DOI: 10.1143/JJAP.47.7936]

Widely tunable terahertz (THz)-wave generation using difference frequency generation (DFG) in an organic N-benzyl-2-methyl-4-nitroaniline (BNA) crystal was demonstrated. To our knowledge, this is the first report of THz-wave generation by BNA DFG. Large, high-quality single crystals of BNA (0 8 mm X 30 mm) were grown using the vertical Bridgman method. The nonlinear optical (NLO) coefficient d(33) of the BNA crystal is similar to 234 pm/V, which is the largest value reported for any yellow NLO material. The collinear phase-matching condition of the type-0 configuration is satisfied using a 0.7-1 mu m band pump wavelength. We generated THz waves using an organic BNA crystal; the generation range is 0.1-15 THz. (C) 2008 Optical Society of America.

The exact power output of a table-top-sized terahertz (THz)-wave source using a nonlinear optical process has not been clarified because detectors for these experiments [Si bolometer, deuterated triglycine sulfate (DTGS), etc.] are not calibrated well. On the other hand, powermeters for the mid-infrared (mid-IR) region are well established and calibrated. We constructed a high-power dual-wavelength optical parametric oscillator with two KTP crystals as a light source for difference frequency generation. The obtained powers of dual waves were 21 mJ at similar to 1300 nm, ten times higher than that of the previous measurement. The device provides high-power THz-wave generation with similar to 100 times greater output power than that reported in previous works. A well-calibrated mid-IR powermeter at similar to 27 THz detected the generated THz wave; its measured energy was 2.4 mu J. Although the powermeter had no sensitivity in the lower-frequency range (below 20 THz), the pulse energy at such a low-frequency region was estimated in reference to the output spectrum obtained using a DTGS detector: the energy would be from about the submicrojoule level to a few microjoules in the THz-wave region. (c) 2007 Optical Society of America.

A wavelength-agile mid-infrared (IR) ZnGeP2 (ZGP) optical parametric oscillator (OPO) using a galvanocontrolled double-crystal KTiOPO4 (KTP) OPO was demonstrated. The mid-IR wavelength was tuned by varying the KTP OPO pump wavelength while the ZGP crystal angle remained fixed. Rapid tuning of the KTP OPO was achieved by changing the crystal angle by using the galvano scanner. Our mid-IR source can jump to a different wavelength without scanning through the intermediate wavelengths while also permitting continuous-wavelength scanning. The mid-IR source can be tuned from approximately 5 to 10 mu m at a phase-matching angle of 51 degrees, while the pump wavelength is controlled in the 1.95-2.2 mu m range. (c) 2007 Optical Society of America.

A photoacoustic microscope (PAM), which includes a condenser microphone and a pair of linear-motordriven pulse stages, was specially designed for spectroscopic applications. The PAM was applied to measure the amount and number of pollen particles of Cryptomeria japonica (CJ), which is known for its allergic function against eyes and nose. The advantage of photoacoustic (PA) imaging is both its high sensitivity and its counting ability up to high concentrations of the specimen. The CJ pollen particles were fixed on a piece of adhesive tape or on albumen (egg white) on a glass slide set in a PA cell. The PA image showed the ability of this method to count CJ pollen from the severalhundred-milligram region to even a single particle. The PA signal obtained was integrated over the specimen surface. The dependence of the PA signal on the amount or number of the pollen particles was measured. The resulting coefficients of correlation of the calibration curves for the amount and the number of pollen particles were 0.94 and 0.97, respectively.

Recently, quality evaluation and control has become increasingly important in biology and agriculture. The evaluation of the quality of food plants has been performed by many inspection methods. To date, the evaluation of the grain of crops by photoacoustic spectroscopy in the infrared region has only been performed for corn. We have developed a method of applying a photoacoustic microscope (PAM) to pollen analysis. In this study, a PAM was used to evaluate the quality of crop grains, rice in this case, for the first time. Due to differences in the absorption of the laser beam, the homogeneity of rice grains was measured and shown as thermal images. The resolution was sufficiently good to evaluate a single grain of rice. This method has an advantage in that it can be used to measure the existence of both the surface and back surface colored regions. In addition to conventional video image evaluation or the macroscopic optical absorption method, PA imaging can enable the evaluation of the quality and condition of rice grains.

We have devised a wavelength-agile mid-IR ZGP-OPO that can rapidly jump to a new wavelength without scanning through intermediate wavelenghts. The mid-IR (5-10 mu m) wavelengths can be scanned by tuning the pump wavelength using a Galvano-controlled double crystal KTP-OPO.

Signal and idlers waves obtained from a Nd: YAG laser pumped KTP optical parametric oscillator (OPO) are difference frequency mixed in a ZnGeP2 (ZGP) crystal to generate radiation in the mid-infrared. The KTP OPO is operated in the type-II phase matching mode, and the extraordinary and ordinary waves are tunable from 1.76 mum to 2.36 mum and from 2.61 mum to 1.90 mum, respectively. The orthogonally polarized waves are difference frequency mixed in a ZGP crystal to generate mid-IR radiation tunable from 5 to 12 mum.

A tunable mid-infrared optical parametric oscillator (OPO) has been demonstrated using a single ZnGeP2 (ZGP) crystal. A KTP OPO was pumped by an Nd:YAG laser to generate 2.02 mum-signal wave at the output, which is used for pumping a singly resonant angle-tuned ZGP OPO to generate mid-IR tunable from 5.5 to 9.3 mum. Maximum pump to idler (2-8 mum) conversion efficiency obtained, was similar to8.25%, which corresponds to similar to32% quantum efficiency. (C) 2004 Elsevier B.V. All rights reserved.

A scanning acoustic microscope (SAM) and a photoacoustic microscope (PAM) operating on a unified software environment was designed and fabricated. Welded steel plates, in which the welding condition was changed by varying the amount of current and its duration, were used as specimens. SAM and PAM measurements for this specimen were carried out, and the obtained images were compared. This system has the advantage of complementary measurement using both SAM and PAM.

In this study, the nondestructive testing (NDT) of tilting surface defects has been demonstrated using a photoacoustic microscope (PAM). The tilting surface defects were fabricated on a metal plane specimen by mechanical processing. The obtained signal strength distribution was affected by the tilt angle of the surface defects, and it is possible to estimate the tilt angle of the surface defects from the gradient of the obtained signal strength distribution.

A photoacoustic microscope (PAM) with linear-motor-drives was designed and fabricated. The PAM has the performance of high spatial resolution, fast scan speed, and quietness at scanning compared used a PAM with conventional pulse-motor slide stages. The PAM was applied to image semiconductor devices and subsurface defects and to measure the amount of the pollen of Cryptomeria japonica (Taxodiaceae). In the former case, the spatial resolution was about 20 mum. In the latter case, PA amplitude image had a good resolution to be resolved up to few single pollen particles. In addition, the obtained PA amplitude image was integrated over the specimen surface, and the integrated signal was measured at various pollen mass. The calibration curve showed the correlation value of 0.94. (C) 2003 Elsevier B.V. All rights reserved.

The amount of pollen of Cryptomeria japonica (CJ), which is known to induce allergic reactions in the eyes and nose, was measured by the use of a photoacoustic (PA) microscope. It was shown that the CJ pollen up to several tens of particles could be measured and that the calibration curve for PA signal versus pollen amount with the correlation coefficient of 0.94 was obtained.

Nondestructive testing (NDT) of metal planes with tilted or variable-depth subsurface defects have been demonstrated using a photoacoustic microscope (PAM). Two types of subsurface defects, the tilted and wedge-shaped vertical ones, were prepared and fabricated in the specimen by mechanical processing. The obtained signal intensity distribution was affected by the tilted and wedge-shaped subsurface defects, and showed an asymmetrical shape.

In this study, the measurement of subsurface defect shape has been demonstrated using photoacoustic microscopy. Two types of subsurface defects are prepared, Using photoacoustic signal intensity distribution with varying thermal diffusion length, the feasibility of the present scheme for estimating the shape of the subsurface defect is shown.

A photothermal deflection microscope using linear-motor-driven slide stages for scanning was designed and fabricated. The photothermal microscope achieved high-resolution scanning (0.1 mum step), fast scanning (40 mm/s) and random access. It operates in a conventional operating software environment as a photoacoustic microscope and is capable of operating in an open-air environment. It was applied to the imaging of semiconductor microdevices such as integrated circuits. Resolution up to 8-12 mum was achieved.

A linear-motor-driven photoacoustic microscope, which realizes both rapid response and quiet environment for a gas-microphone detection system, is fabricated as a candidate for the optimum gas-microphone photoacoustic microscopy system.