Takuya Mikami

Sellmeier and thermo-optic dispersion formulas for β-BaB2O4 (revisited)

This paper reports the high-accuracy Sellmeier and thermo-optic dispersion formulas for β-BaB2O4 (β-BBO) that provide the excellent reproduction of our data for second-harmonic generation (SHG) and sum-frequency generation (SFG) down to 0.2048 and 0.1925μm as well as the optical parametric oscillator (OPO) tuning points up to 3.2μm, and the temperature-dependent phase-matching angles for SHG and SFG that we have measured in the 0.193-0.6420μm range as well as the recent data for SFG at 0.1934μm.

Set of Sellmeier equations for GaS and GaSe and its applications to the nonlinear optics in GaS(x)Se(1-x).

This paper reports a set of Sellmeier equations for GaS and GaSe that provide excellent reproduction of the phase-matching conditions for second- to sixth-harmonic generation of CO₂ laser radiation at 10.5910 μm in GaS(0.4)Se(0.6) at 20°C. In addition, this set of Sellmeier equations is found to reproduce well the phase-matching angles for second-harmonic generation of a Ti:Al₂O₃ laser-pumped BaB₂O₄ optical parametric generator at 2.14-2.9 μm and CO₂ laser radiation at 9.2(9.2007)-10.7(10.6746)  μm measured by Kang et al. [Appl. Phys. B 108, 545 (2012)] in GaS(0.09)Se(0.91) and GaS(0.41)Se(0.59).

Fourth-harmonic generation of the CO2 laser wavelength at 10.5910 μm in BaGa4S7

This paper reports the 90° phase-matched fourth-harmonic generation of the CO2 laser wavelength at 10.5910 μm in BaGa4S7. The 1.4 cm long BaGa4S7 crystal used in the present experiment was cut at θ=9.2° in the xz(=bc) plane. The pump source was the second harmonic of the wave-guide CO2 laser (10.5910 μm) operating with an average output power of 18.3 W at 130 kHz. By focusing the 7.6 W, 5.2955 μm pulses (peak power is 6kW with 10 ns pulse duration) generated from the 2 cm long AgGa0.65In0.35Se2 crystal into the BaGa4S7 crystal (θPM=9.9°) with the 6 cm focal length ZnSe lens, the maximum average output power of 0.3 W was obtained at 2.6478 μm without any damage to the crystal. In addition, the new Sellmeier equations of BaGa4S7 are presented.

Direct third-harmonic generation in BiB3O6

The 90° phase-matched direct type-1 and type-2 third-harmonic generation (THG) at 0.3263 and 0.3837 μm were observed along x of the monoclinic BiB3O6 at room temperature by using the idler of the β-BaB2O4 parametric oscillator. These interactions preclude the non-phase-matched, cascaded quadratic processes owing to the crystal symmetry along x. The phase-matching properties for these pure cubic processes are presented together with the results on the direct THG of the Nd:YAG laser at 1.0642 μm in three principal planes.

Second-harmonic generation in Hg0.35Cd0.65Ga2S4 and Hg0.52Cd0.48Ga2S4

Hg0.35Cd0.65Ga2S4 and Hg0.52Cd0.48Ga2S4 have been found to be phase-matchable for type-1 second-harmonic generation (SHG) of the fundamental radiation at 2.907-5.453 μm and 2.423-6.725 μm, respectively. The Sellmeier equations for HgGa2S4 and CdGa2S4 that reproduce well these experimental results as well as the published data for the Cr:forsterite laser (1.25 μm)-pumped Hg0.35Cd0.65Ga2S4 optical parametric generator (OPG) and the Ti:Al2O3 laser (0.820 μm)-pumped Hg0.52Cd0.48Ga2S4 optical parametric amplifier (OPA) at 5.59-9.12 μm are presented.

Ion-assisted coating for large-scale Bimorph deformable mirror

We have fabricated a 410 x 468 mm size deformable mirror with 100 Bimorph piezoceramic actuators for the LFEX laser system at Osaka University. In the case of Bimorph-type deformable mirrors, the mirror surface had to be polished and coated after bonding the piezoceramic actuators to the rear side of the thin mirror substrate. This provides a good surface figure, but the coating temperature for the high-reflection mirror was strictly limited because of the thermal fragility of piezoceramic actuators. The mirror substrate with the actuators was polished, and an ion-assisted multilayer dielectric coating was produced at 60 degrees Celsius with our 80-inch coating chamber. The flatness of the mirror just after coating was 7 μm, and reduced by aging to 3.2 μm when the mirror was assembled. The surface figure of the assembled mirror with 20 piezostack bonded actuators is demonstrated and a laser-induced damage threshold tested with a witness sample is also reported.

High-accuracy sellmeier equations for GaS x Se 1−x (x=0, 0.09, 0.40, and 1)

This paper reports the high-accuracy Sellmeier equations for GaS_xSe_1-x (x=0, 0.09, 0.40, and 1) that provide excellent reproduction of the phase-matching angles for SHG to 5HG of CO₂ laser radiation at 10.5910 μm in GaS_xSe_1-x (x=0, 0.40, and 1) [1] as well as SHG of a Ti:Al₂O₃ laser-pumped BBO/OPG at 2.14-2.9 μm and CO₂ laser radiation at 9.2-10.7 μm achieved in GaS_xSe_1-x (x=0.09 and 0.41) [2,3].

90° Phase-matched difference-frequency generation at 5.34–7.48 μm in BaGa 4 S 7

By pumping the 1.4 cm long θ=9.2° and φ=0° cut BaGa₄S₇ crystal oriented for the 90° phase-matching conditions along the z(=b) axis with the Quanta Ray GLR-20 Nd:YAG laser incorporating the BBO/OPO and by changing the crystal temperature from 25 °C to 180 °C, we have generated the tunable mid-IR pulses in the 5.341-7.477 μm range.

Modified Sellmeier equations for ZnGeP2 in the 0.97-1640μm range

This paper reports the modified Sellmeier equations for ZnGeP2 (ZGP) that provide excellent reproduction of the phase-matching conditions for DFG between the two CO2 laser wavelengths, and the Nd:YAG laser and the Nd:YAG laser-pumped OPO in the THz region. Model calculations based on these Sellmeier equations strongly indicate that there is no significant difference in the refractive indices of the non-annealed and annealed crystals from 1.0642μm to 1640μm (0.18THz).