Kentaro Miyata

Phase-matched pure χ (3) third-harmonic generation in noncentrosymmetric BiB 3 O 6

Third-harmonic generation (THG) has been investigated in the monoclinic BiB3O6. The symmetry and birefringence analysis revealed that there are phase-matching conditions for the direct third-order nonlinear process, where the cascading second-order processes are precluded by the zero effective nonlinearity. The first phase-matched pure χ(3) THG in a noncentrosymmetric crystal is presented together with the improved Sellmeier and thermo-optic dispersion formulas.

High-efficiency single-crystal third-harmonic generation in BiB 3 O 6

Third-harmonic generation of high-intensity, sub-100-fs idler pulses from a Ti:sapphire-laser-pumped optical parametric amplifier is demonstrated by using a single nonlinear crystal of BiB₃O₆ (BIBO). Maximum internal energy conversion as high as 11% from the fundamental to the third harmonic is achieved by phase- and group-velocity matching for the direct cubic nonlinear process together with the velocity-mismatched cascading quadratic processes.

Picosecond mid-infrared optical parametric amplifier based on the wide-bandgap GaS 0.4 Se 0.6 pumped by a Nd:YAG laser system at 1064 nm

Operation of a GaS(0.4)Se(0.6) optical parametric amplifier is demonstrated with a 5-11 μm idler tuning range, maximum energies of ∼10 μJ for sub-30-ps pulse durations, and performance ∼3 times better than with pure GaSe.

Phase-matching properties for AgGaGeS4

The phase-matching conditions of AgGaGeS(4) have been measured for second-harmonic generation at 0.8 and 5.3 microm, and difference-frequency generation at 2.2, 3.6-5.1, and 4.8-11.8 microm. The improved Sellmeier equations that reproduce well the various phase-matching conditions are presented.

Temperature phase-matching properties for harmonic generation in GdCa 4 O(BO 3 ) 3 and Gd x Y 1-x Ca 4 O(BO 3 ) 3

GdCa4O(BO3)3 has been found to have phase-matching points where the temperature variations of the phase-matching angles become zero for type-1 sum-frequency generation in the zx plane. We also found that the temperature sensitivities of the phase-matching conditions in the zx plane are different along the phi = 0 degrees and phi = 180 degrees directions in this material. In addition, the thermo-optic dispersion formula of this material that reproduces the temperature phase-matching properties of GdCa4O(BO3)3 and Gd(x)Y(1-x)Ca4O(BO3)3 is presented.

Some properties of the mixed GaS0.4Se0.6 nonlinear crystal in comparison to GaSe

Two essential advantages can be expected from adding S to the well known nonlinear crystal GaSe: increase of the bandgap value or the short wave cut-off limit and improved hardness. Recently, we confirmed that the non-centrosymmetric structure of GaSe is preserved up to a GaS content of 40 mol. % while the nonlinear coefficient d22 is reduced by only 24%. The increased band-gap results also in higher surface damage threshold. Our preliminary Sellmeier equations for GaS0.4e0.6 were based on refractive index measurements. These equations are refined in the present work by fitting second-harmonic generation and optical parametric amplification phase-matching angle data in the mid-infrared as well as birefringence data in the visible and near-infrared obtained with thin phase retardation plates. The two-photon absorption effect was studied for GaS0.4e0.6 and GaSe using amplified picosecond pulses at 1064 nm, at a repetition rate of 10 Hz. For intensities in the GW/cm2 range, the two-photon absorption coefficient of GaS0.4e0.6 for the o-polarization is 3.5 times smaller than the corresponding coefficient of GaSe. This means that GaS0.4e0.6 could be safely used in Nd:YAG laser pumped nanosecond optical parametric oscillators or picosecond optical parametric amplifiers, without nonlinear absorption losses. The dynamic indentation measurements with Berkovich type indenter of c-cut GaS0.4e0.6and GaSe plates indicate about 30% higher indentation modulus and microhardness of GaS0.4e0.6 in comparison to GaSe.

Simultaneously phase-matched blue and red light generation using BIBO.

BiB3O6 has been found to be simultaneously phase matchable for sum-frequency generation at 0.4627 and 0.6260 microm by mixing the outputs of a 0.5321 microm pumped parametric oscillator with the fundamental source at 1.0642 microm. The simultaneous blue and red light generation is achieved under the temperature-insensitive phase-matching condition, and the relative strength of blue and red light can be controlled by changing the effective nonlinear constants through the azimuth angle. In addition, wide wavelength tuning of the simultaneous phase matching is obtained by the use of a noncollinear geometry, enabling a compact red-green-blue laser system based on the powerful solid-state laser.

Nd:YAG laser pumped HgGa2S4 parametric oscillator

By pumping the 8mm long HgGa2S4 crystal cut at θ = 67.5° and φ = 0° with the Nd:YAG laser in the double-pass SRO (singly resonant oscillator) scheme, we have generated 410mW output power (80mW at 4.180μm and 330mW at 1.428μm) at 30Hz. The pump to output conversion efficiency was 17%. In addition, by heating the HgGa2S4 crystal from 20° to 120° at normal pump incidence (θpm = 67.5°), we have generated the tunable outputs in the 1.413～1.428μm and 4.180～4.311μm range.

Efficient Frequency Doubling of a Low-Power Femtosecond Er-Fiber Laser in BiB

BiB3O6 (BIBO) crystal has been used for efficient second-harmonic generation (SHG) of a low-power femtosecond Er-fiber laser-amplifier system operating at 56 MHz. At the maximum input power of 65 mW, an internal conversion efficiency of 23% was achieved for SHG at 782 nm, with a pulse duration of 64 fs. A comparison with beta-BaB2O4 reveals superior properties of BIBO for such ultrashort-pulse ultra-broadband SHG.

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Thermo-optic constants for BiB/sub 3/O/sub 6/ were measured from 20.0 to 120.0/spl deg/C at 0.5435 and 1.0642 /spl mu/m. The thermo-optic dispersion formula that reproduces well the temperature-dependent phase-matching conditions in the 0.3547-1.621 /spl mu/m is presented.