Frequency conversion of femtosecond Ti:Sapphire laser pulse into 5–11 μm wavelength range with ZnGeP2, AgGaS2 and LiGaS2crystals

An ultrashort-pulse mid-infrared laser system tunable within a wavelength range of ∼ 5–11 μm is experimentally demonstrated. The system is based on difference frequency generation in a nonlinear crystal, where a Ti:Sapphire pump beam is mixed with a signal pulse formed through self-phase modulation of the Ti:Sapphire laser pulse under its filamentation in a CO2 gas cell. Three nonlinear crystals were examined in this setup: ZnGeP2, AgGaS2, and LiGaS2. Central wavelength tuning from ∼ 5.5 μm to ∼ 10 μm was carried out with AgGaS2 and LiGaS2 crystals. The LiGaS2 crystal provided the highest mid- infrared pulse energy of 2.7 μJ at 6 μm wavelength and broadband pulse spectrum within 7.5–11.5 μm wavelengths. The ZnGeP2 crystal provided the highest efficiency of 0.16 % for frequency conversion into ∼ 10 μm wavelength region, but that took place at low pump pulse energy/intensity (0.3 mJ/∼30 GW/cm2), which, being higher, resulted in lower efficiency due to nonlinear absorption.