Efficient frequency doubling of ps-pulses from a free-electron laser in ZnGeP2☆

Abstract We report second-harmonic generation in ZnGeP 2 in the mid-IR using a high power, short pulse, free-electron laser. For fundamental wavelengths between 5.5 to 9.0 μm external efficiencies for second-harmonic generation up to 49% have been reached, which is close to the theoretical limit. At longer wavelengths the efficiency is reduced as a result of absorption in the crystal.