Parametric frequency converters with LiInSe_2, AgGaGeS_4, HgGa_2S_4 and Hg_(0.65) Cd_(0.35)Ga_2S_4 crystals

摘要

Second harmonic generation of 9 μm emission band of CO_2 laser is for the first time realized with a number of new nonlinear crystals: biaxial LiInSe_2, AgGaGeS_4 (that is solid solution AgGaS_2:GeS_2 or Ag_xGa_xGe_(1-x)S_2, or AgGaGe_xS_2(1+x) at x=0.5) and uniaxial HgGa_2S_4, Cd_(0.35)Hg_(0.65)Ga_2S_4 (solid solution HgGa_2S_4:CdGa_2S_4 with mixing ratio x=0.35). For LiInSe_2 and AgGaGeS_4 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 CO_2 laser pulses at 9.55 μm is determined as 1.7 to 2.3 times higher than for popular middle IR crystals such as ZnGeP_2 or AgGaSe_2. Parameters of second harmonic generation were determined correctly in comparison with ZnGeP_2 crystals at 33 ns pump pulses and intensities that are about 28.5% (40 MW/cm~2) of damage thresholds of ZnGeP_2. As high as 7% external peak power efficiencies (4.7% in energy) is typical for orange and yellow phases of 3.1 mm HgGa_2S_4 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 AgGaGeS_4 crystal at pump intensities that is only 11% of damage threshold. Its were determined phase-matching angles, spectral dependence of second harmonic generation efficiencies, so as angular and spectral phase-matching widths that are investigated in details.