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

Abstract

High-power infrared laser systems with broad-band tunability are of great importance due to their wide range of applications in spectroscopy and free-space communications. These systems require nonlinear optical (NLO) crystals for wavelength up/down conversion using sum/difference frequency generation, respectively. NLO crystals need to satisfy many competing criteria, including large nonlinear optical susceptibility, large laser-induced damage threshold (LIDT), wide transparency range, and phase-matchability. Here, we report bulk single crystals of SnP2S6 with a large nonresonant SHG coefficient of d33 = 53 pm V–1 at 1550 nm and a large LIDT of 350 GW cm–2 for femtosecond laser pulses. It also exhibits a broad transparency range from 0.54 to 8.5 μm (bandgap of ∼2.3 eV) and can be both Type I and Type II phase-matched. The complete linear and SHG tensors are measured as well as predicted by first-principles calculations, and they are in excellent agreement. Two relatively flat conduction bands in the electronic band structure are shown to enhance the nonresonant SHG response through a double resonance enhancement of the nonresonant optical response. Therefore, SnP2S6 is an outstanding candidate for infrared laser applications.