Journal of Nonlinear Optical Physics & Materials Vol. 22, No. 3 (2013) 1350033 (9 pages) c  World Scientific Publishing Company DOI: 10.1142/S0218863513500331 OPTICAL PARAMETRIC INTERACTION IN INFRARED REGION CRYSTALS RENA J. KASUMOVA Physics Department, Baku State University, Z. Khalilov str. 23, AZ1148, Baku, Azerbaijan rkasumova@azdata.net Received 4 August 2013 In this work, parametric interaction is investigated with the account for phase change of interacting pump, signal and idler waves in the materials of infrared (IR) range of spectrum in case of Zn 1-x MgxSe crystal. We give an analysis of the threshold intensity of pumping for Zn 0.75 Mg 0.25 Se crystal under conditions of the existing experiment, as well as the analytical expression for obtaining the optimum value of phase mismatch ∆opt , at which maximum of signal wave reinforcement is reached. The values of refractive indices, angle of phase matching and angular dispersion coefficient of the first-order for Zn 0.52 Mg 0.48 Se have been calculated. Keywords : Parametric interaction; IR region; constant-intensity approximation. PACS Number(s): 42.65.-k, 42.65.Yj, 42.70.Mp, 42.79.Nv 1. Introduction The infrared (IR) region of spectrum is interesting besides the various technical uses for application by existence of two atmospheric windows. The optical parametric generators of this range are successfully used for the tasks of spectroscopy, on their base LIDARs, in particular for investigation of the Earth and atmosphere. It is related to the fact that, as a rule, the oscillatory spectra of molecules are found in this region of spectrum. Tunable parametric sources of coherent radiation in combination with the effects of frequency mixing permit to extend considerably the field of tunable wavelengths of laser radiation. The optical multipliers of frequency serve this task too. As is known by the choice of crystals — converters of frequency — the main selection condition is, on the one hand, their transparency in the broad region of spectrum, on the other hand, their high nonlinear susceptibility in comparison with the existing crystals. CdGeAs 2 , ZnGeP 2 , GaAs and AgGaS 2 crystals are the efficient nonlinear crystals for mid-IR region of spectrum. 1,2 It is also possible to note the prospect hexagonal crystals of A II B VI class. For instance, hexagonal single crystals of CdS and CdSe compounds and their solid solutions CdS 1-x Se. 3 As an 1350033-1