Tunable and coherent nanosecond radiation in the range of 2.7–28.7 μm based on difference-frequency generation in gallium selenide

Continuously tunable and coherent radiation in the mid-IR range of 2.7–28.7 μm has been achieved in GaSe through type-I difference-frequency generation (DFG). The two mixing beams used for the DFG consist of the idler beam (0.73–1.8 μm) of an optical parametric oscillator pumped by the nanosecond Nd:YAG laser and the residual Nd:YAG fundamental beam (1.064 μm). The maximum peak output power for type-I DFG is measured to be 2.2 kW at the wavelength of 4 μm. Moreover, the type-II DFG with the kilowatt peak power and output wavelength continuously tunable in the range of 4.14–28 μm has also been achieved.