SnP2S6: A Promising Infrared Nonlinear Optical Crystal with StrongNonresonant Second Harmonic Generation and Phase-Matchability

High-power infrared laser systems with broad-band tunability are of greatimportance due to their wide range of applications in spectroscopy and free-spacecommunications. These systems require nonlinear optical (NLO) crystals for wavelengthup/down conversion using sum/difference frequency generation, respectively. NLO crystalsneed to satisfy many competing criteria, including large nonlinear optical susceptibility, largelaser-induced damage threshold (LIDT), wide transparency range, and phase-matchability.Here, we report bulk single crystals of SnP2S6with a large nonresonant SHG coefficient ofd33=53pmV-1at 1550 nm and a large LIDT of 350 GW cm-2for femtosecond laser pulses. Italso exhibits a broad transparency range from 0.54 to 8.5 mu m (bandgap of similar to 2.3 eV) and canbe both Type I and Type II phase-matched. The complete linear and SHG tensors aremeasured as well as predicted byfirst-principles calculations, and they are in excellentagreement. Two relativelyflat conduction bands in the electronic band structure are shown toenhance the nonresonant SHG response through a double resonance enhancement of thenonresonant optical response. Therefore, SnP2S6is an outstanding candidate for infrared laserapplications