Analyses of phase-matching parameter in difference frequency generation with AgGaS2 and AgGaSe2

Interesting in generation and exploration of mid-infrared radiation has induced using optical parametric effect in nonlinear optical crystal with high nonlinearity, high transmission, phase-matching ability, and high sensitivity in room temperature, such as AgGaSe2(AGSe), AgGaS2(AGS) crystals. To achieve mid-infrared radiation, we use difference frequency generation (DFG) in AGS or AGSe crystals by pumping with the output of optical parametric oscillator. The mid-infrared radiation tunable characteristics of AGS and AGSe crystals under type-I phase-matching have been analyzed based on optical parameter DFG theory. Beam walk-off angle and acceptance angle limit conversion efficiency and restrict the DFG tuning wavelength range. We focus to research for effective nonlinear coefficient, walk-off angle and acceptance angle as functions of wavelength, the relationship between conversion efficiency and acceptance angle, and crystals length impact on the process of frequency conversion. We obtained 10 μm wavelength with a 10 mm crystal length, 1030nm pump, walk-off angles and acceptance angles of AGS and AGSe crystals are 1.19°and 0.68°, 0.107°and 0.171°respectively. Results are very useful for mid-infrared experimental studies on AgGaS2 and AgGaSe2 crystals.