Parametric frequency converters with LiInSe 2 , AgGaGeS 4 , HgGa 2 S 4 and Hg 0.65 Cd 0.35 Ga 2 S 4 crystals

Abstract

Second harmonic generation of 9 μm emission band of CO₂ laser is for the first time realized with a number of new nonlinear crystals: biaxial LiInSe₂, AgGaGeS₄ and uniaxial HgGa₂S₄, Cd_0.35,Hg_0.65Ga₂S₄. For LiInSe₂ and AgGaGeS₄ it is first type of frequency conversion realized some time or other. Main feature of this crystals is wide range transparency from 0.4-0.6 to 12.5-16.2 μm. Their damage thresholds for 30 ns TEA CO₂ laser pulses at 9.55 μm is determined as 1.7 to 2.3 times higher than for popular middle IR crystals such as ZnGeP₂ or AgGaSe₂. Parmateters of second harmonic generation were determined correctly in comparison with ZnGeP₂ crystals at 33 ns pump pulses and intensities that are about 28.5% of damage thresholds of ZnGeP₂. As high as 7% external peak power power efficiencies is typical for orange and yellow phases of 3.1 mm HgGa₂S₄ crystal at such pump that is only 13% of its damage threshold. Efficiencies as high as 0.45% and 0.3% are realized in 2.1 mm AgGaGeS₄ crystal at pump intensities that is only 11% of damage threshold. It was determined phase-matching angles, spectral dependence of second harmonic generation efficiencies, so as angular and spectral phase-matching widths that are investigated in details.