宮本 克彦

We developed a high average power, diffraction-limited (M2∼1.1) picosecond laser system formed of a sapphire face-cooled Nd:YVO4 slab amplifier with a multi-pass geometry. Average output power of 46.4 W was obtained at an optical-optical efficiency of 56%.

We demonstrate a broadband, highly intense 0.6-terahertz vortex pulse by utilizing a polymeric Tsurupica spiral phase plate.

We present the first demonstration of the ultrahighly efficient second harmonic generation of an optical vortex pulse. An optical-optical efficiency of &gt 70% frequency-doubled vortex output was obtained.

We have demonstrated a tunable mid-infrared optical vortex generation by an optical vortex pumped 2 mu m optical parametric oscillator in combination with a AgGaSe2 difference frequency generator. The lasing wavelength of the vortex output was tuned within a 'whole mid-infrared' wavelength region of 6-18 mu m.

Optical vortex illumination enables the creation of silicon needles with a height of similar to 14 mu m and a thickness of similar to 2 mu m. Silicon needle formation requires an optical vortex pulse with a pulse duration of 10 similar to 20 ps, so as to create thermally-melted silicon with fewer heat diffusion effects.

We developed an octave-band tunable optical vortex laser based on a 0.532-mu m optical vortex-pumped optical parametric oscillator with an extended cavity configuration by employing cascaded non-critical phase-matching LiB3O5 crystals. The optical vortex output was tuned within a wavelength range of 735nm-1893nm, and a pulse energy of 0.24-2.36 mJ was also achieved.

We demonstrate highly intense, monocycle 0.6-terahertz (THz) vortex generation by utilizing a Tsurupica spiral phase plate in combination with a tilted-pulse front pumping optical rectification THz generator formed of a prism-cut LiNbO3 crystal. A maximum THz vortex pulse energy of 2.3 mu J was obtained.

Handedness control of the mid-infrared vortex output from a ZnGeP2 difference frequency generator pumped by a 1-mu m vortex pumped KTiOPO4 optical parametric oscillator was demonstrated over a frequency range of 9-12 mu m.

We developed a widely tunable 1-mu m optical vortex laser formed of a 0.5-mu m vortex pumped optical parametric oscillator by employing non-critical phase-matching LiB3O5 crystals. Tunable vortex output was obtained in the wavelength range of 880-1345nm.

Fractional vortex lasers with a fractional topological charge, l, exhibiting a unique fractional radial opening, have been attractive for the optical manipulating of microscopic particles and super-resolution spectroscopy based on stimulated emission depletion. They have also recieved much attention in fundamental physics, including an analogy concerning the quantum flux in the Aharonov-Bohm effect. Such applications of the fractional vortex lasers frequently require wavelength diversity. In particular, tunable fractional vortex lasers in a mid-infrared region, including the eigen frequencies of many molecules originating by the vibration modes, will potentially be attractive for manipulating molecules and molecular spectroscopy with high spatial resolution. Second-order nonlinear frequnecy conversion is a promising method to extend the wavelength range of laser sources. However, the conservation of topological charge, l, in an optical parametric down-conversion process causes a question, i.e., how does the orbital angular momentum of the pump beam divide between the signal and idler outputs? To date, we have demonstrated 2μπι fractional vortex output with a topological charge l=0.5 from a 1μm vortex pumped optical parametric oscillator (2μπι fractional vortex OPO) formed by a plane-parallel cavity configuration and a nonlinear crystal KTP [1]. (Such the fractional optical vortex operation is never permitted in a conventional stable laser cavity [2].) However, the pulse energy (<;0.5mJ) of the fractional vortex output is limited by severe diffraction loss in the plane-parallel cavity configuration. Also, the lasing wavelength of the fractional vortex output was fixed at 2.128μm.

We presented the first demonstration of the helicity control of the optical vortex output from a vortex-pumped optical parametric oscillator by inverting the wavefront helicity of the pump vortex beam.

We have developed a picosecond terahertz light source with a wide tunability (1-15THz) and a narrow linewidth (similar to 120GHz) formed by a 1 mu m picosecond laser, a fan-out PPSLT optical parametric amplifier and a DAST crystal.

graphene with its unique electric, thermal, and optical properties has proven to be a promising candidate for many of the next generation electronics application. In this report, we try to provide a clear undeniable evidence that proves our success in the development of a THz nano-sensor using the graphene nano-carbon material as a mean to utilize the thermoelectric current that can be generated due to the bolometric effect at room ambient conditions.

We discovered that chiral-structure of nano-needles fabricated by optical vortex laser ablation can be controlled by changing the magnitude of orbital angular momentum. We also demonstrated the formation of a chiral Si-bump.

We demonstrated for the first time an ultra-violet vortex output without a spatial separation of phase singularities by frequency-doubling a green vortex laser with a pair of β-BaB2O4 and reversed β-BaB2O4 crystals. © 2013 IEEE.

Optical vortex modes, possessing a spiral wavefront, an annular intensity profile and orbital angular momentum, mh (m is termed a topological charge), have been intensely investigated in various applications, such as an optical tweezer, quantum information processing, and laser ablation. Recently, we discovered that the wavefront helicity (clock-wise or counter clock-wise spiral direction) of the optical vortex can be transferred to melted metal through a laser ablation process, forming chiral metal nanoneedles [1]. These nanoneedles will open the possibility of new structured materials, such as chiral planer metamaterials. © 2013 IEEE.

We demonstrated high energy 2 mu m optical vortex pulse production from an optical vortex pumped hemispherical optical parametric oscillator. Maximum 2 mu m optical vortex pulse energy of 2.1 mJ was achieved.

26.5W of nanosecond vortex laser based on a stressed Yb-doped fiber amplifier was demonstrated. The peak power of 70 kW was obtained, corresponding to optical-optical efficiency of 41 %. (C)2012 Optical Society of America

A method for simultaneously measuring the refractive index and absorption coefficient of nonlinear optical crystals in the ultra-wideband terahertz (THz) region was developed. 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 DAS were experimentally determined in the frequency range of 2.5-26.2 THz.

Widely tunable terahertz (THz) -wave generation using difference frequency generation (DFG) in an organic N-Benzyl-2-methyl-4-nitroaniline (BNA) crystal was demonstrated. An organic nonlinear optical (NLO) BNA crystal is one of the promising materials for efficient and strong THz-wave generation because of its potential to have a sufficiently large enough second-order optical nonlinearity. Large and high quality single crystals of BNA (phi 8x30mm) were successfully grown by a vertical Bridgman method. The NLO coefficient d(33) of BNA crystal is about 230pm/V. It is the largest value reported for any yellow-colored NLO materials. BNA has low refractive index dispersion between the optical and THz-wave region, therefore the colinear phase matching condition of the Type0 configuration is satisfied by using 0.7 similar to 1 mu m band pump wavelength. So, we developed a near-infrared dual-wavelength pump source for BNA-DFG. Two KTiOPO4 (KTP) crystals were mounted on galvano scanners inside a double-pass optical parametric oscillator (OPO). It is pumped using a frequency-doubled Nd:YAG laser (532 nm, 8 ns, 100 Hz). The signal wave of the KTP-OPO output was controlled independently and rapidly using a galvano scanner. We successfully generated THz-wave using organic BNA crystal. The THz-wave generation range is from 0.1 to 15THz, while the pumping dual-wavelength is controlled in the 0.8-0.9 mu m range.

We demonstrate ultrabroadband THz wave detection using a photoconductive antenna with it combination of an ultrashort pulsed laser with 5 fs pulse duration and a DAST crystal. We successfully detected an extremely wide frequency range from 0.5 to 170 THz.

We demonstrate ultrabroadband THz field detection with a photoconductive antenna using a combination of ultrashort laser pulses of 6fs duration and a DAST crystal. We successfully observed ultra-high frequency component beyond 170THz in near-infrared region. (C)2008 Optical Society of America

We demonstrate widely tunable terahertz-wave generation using difference frequency generation (DFG) in an organic N-benzyl-2-methyl-4-nitroaniline (BNA) crystal. The frequency tuning of the BNA-DFG was obtained between 0.1 and 15 THz. © 2008 Optical Society of America.

We report the demonstration of a wavelength-agile coherent tunable mid-infrared (IR) ZnGeP2 (ZGP) optical parametric oscillator (OPO). The mid-IR wavelength was tuned by varying the KTiOPO4 (KTP) OPO pumping wavelength, while the ZGP crystal angle remained fixed. The wavelength of pump OPO was controlled by changing the KTP crystals angle using a Galvano-optical beam scanner. Our mid-IR source can jump to a arbitrary wavelength without scanning through the intermediate wavelengths. A nonlinear optical crystal ZGP is suitable for OPOs in the mid-IR region. In most cases of mid-IR light generation using an OPO, the wavelength tuning is achieved by controlling the phase-matching angle or temperature of the nonlinear optical crystal. However, there are several disadvantages of this method including the walk-off angle, beam pass instability, refraction losses due to the high refractive index of ZGP (n similar to 3.1), slow tuning rate, and so forth. Therefore, we developed a 2-mu m-band pump-wavelength tunable mid-IR ZGP-OPO source. The mid-IR wavelength from the ZGP-OPO could be tuned from 5 to 9.8 mu m, when the pump wavelength was controlled from 1.95 to 2.3 mu m. The output pulse energy at 8 mu m was 1.3mJ/pulse at repetition rate of 30Hz. As an application of random wavelength accessibility, we could achieve the real-time measurement of phase change (solidification) of candle wax by measuring the change of absorption at two arbitrary wavelengths. We selected two wavelengths on the spectrum where significant changes of absorption upon solidification were detected and performed two-wavelength absorption measurements as the sample is allowed to cool from melted state.

Effective and widely tunable THz-wave generation using difference frequency generation in an organic 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) was demonstrated by optimization of optical wavelength with respect to each THz-wave frequency.

The THz region is well-matched to the low-frequency motions of molecules. THz pulsed imaging and spectroscopy are powerful tools for exploring biological, chemical, pharmaceutical fields. For these purposes, we developed a widely tunable and frequency-agile monochromatic THz source spanning from 1.5 to 60THz, using nonlinear optical processes. By using the organic crystal 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST), we succeeded in the generation of THz-wave tunable of broad spectrum (1.5-47THz). In addition to, 30-60THz was also generated by using a semiconductor crystal ZnGeP2 (ZGP) with large output of ∼mJ order. In these experiments, we used frequency-agile KTP-OPO pumping source controlled by a Galvano-scanner. ©2006 IEEE.

We demonstrate wavelength-agile mid-IR ZGP-OPO. The wavelength was tuned by varying the KTP-OPO pump wavelength, while the ZGP crystal angle remained fixed. The KTP-OPO was rapidly tuned by changing the crystal angle using a Galvano-scanner. ©2006 Optical Society of America.