Efficient generation of the second harmonic of CO₂laser radiation in a GaSe crystal

Abstract

Efficient generation of the second harmonic of CO 2 laser pulses was achieved in GaSe single crystals at repetition frequencies up to 100 Hz. The phase-matching angles were measured for GaSe at pump wavelengths of 9.3, 9.6,10.3, and 10.6/zm. The threshold power densities for surface optical damage and for the formation of a plasma jet on the surface of GaSe were determined. The efficiency of second harmonic generation in a GaSe crystal 0.65 cm thick was up to 9%. A comparison was made of GaSe and ZnGeP 2 crystals as materials suitable for the generation of the second harmonic of CO 2 laser radiation.

High-Quality GaSe Single Crystal Grown by the Bridgman Method

“…The infrared-transmission spectrum is shown in Figure 3 a, and the infrared transmittance is about 66% over the all range from 500 to 4000 cm −1 , which is the highest ever reported for GaSe crystals grown by the Bridgman method. The optical absorption coefficient was calculated by the equation in [ 29 , 30 ]. The absorption coefficient is as low as 0.18–0.2 cm −1 in the range of 0.9–14 μm (see Supplementary Materials, Figure S2 ), indicating the perfect optical quality of GaSe sample.…”

Parametric generation of tunable infrared radiation in ZnGeP_2 and GaSe pumped at 3 μm

“…Semibe effectively used for purposes of CO 2 laser frequency tor uniaxial crystals ZnGeP 2 (point group 42m) and doubling. 25 The first OPG that used GaSe 4 was demon-)oint group 62m) both have band gaps in the visible strated in a traveling-wave geometry by means of 100-ps re grown by use of the Bridgman-Stockbarger pulses from an Er:YAG laser (2.94 jim) with the tuning IR dye-laser pulses in a GaSe crystal. The energy of mid-3s higher than the corresponding value for LiNbO 3 IR pulses was of the order of microjoules, and the photon times higher than that for AgGaS 2 .…”

“…These lasers are well suited as pumping sources for parametric devices based on ZnGeP 2 and GaSe crystals because of the good transparency of these nonlinear crystals (absorption coefficient <0.1 cm-') and the small amount of Stokes losses (compared with 1.06-jimpump radiation) resulting from the smaller difference between pump and idler photon energies (and leading to a larger absolute conversion efficiency at a given quantum efficiency), the absence of two-photon absorption, and the existence of the phase-matching conditions for three-wave interactions in the whole transparency region. The laser used in this study was based on flash-lamppumped Er3+:YAG (A = 2.94 jim) 27 or Er'+:Cr'+:YSGG crystal (A = 2.79 im) 25 with typical dimensions of 04 x (80-110) mm. A schematic of an actively mode-locked Er laser is shown in Fig.…”

Transition from parabolic to ring-shaped valence band maximum in few-layer GaS, GaSe, and InSe

“…The III-VI group semiconducting layer compounds GaS, GaSe, and InSe were discovered in the 1930s [1][2][3] but attracted considerable attention only in the 1950s-1980s due to their strong structural anisotropy [4][5][6][7][8] and remarkable nonlinear optical properties [9][10][11][12][13][14][15][16][17][18]. Each layer of these materials has a hexagonal symmetry and is composed of two planes of metal atoms, sandwiched between two chalcogen planes.…”