“Two-Color” Difference Frequency Generation Due to Type-I and Type-II Phase Matching in a Nonlinear BaGa2GeS6 Crystal Pumped by Femtosecond Ti:Sapphire Laser Pulses

The difference frequency generation of femtosecond Ti:sapphire laser pulses in the wavelength range of 5‒10 μm in a 2.46-mm-long nonlinear BaGa2GeS6 crystal has been experimentally studied. The energy of difference frequency radiation pulses has reached 23 μJ. It has been found that “two-color” difference frequency generation occurs in BaGa2GeS6 simultaneously due to type-I and type-II phase matching, leading to the appearance of two ~0.5 μm wide spectral bands in the mid-infrared range separated by 1.5–2 μm. The influence of the polar and azimuthal angles of BaGa2GeS6 on the spectral and energy characteristics of the two-color radiation has been demonstrated. The resulting two-color radiation can be used for remote gas analysis by the differential absorption method.