SnP$_2$S$_6$: A Promising Infrared Nonlinear Optical Crystal with Strong Non-Resonant Second Harmonic Generation and Phase-matchability

TL;DR

This paper introduces SnP₂S₆ crystals as highly effective infrared nonlinear optical materials with strong second harmonic generation, broad transparency, and high damage threshold, suitable for advanced laser applications.

Contribution

It reports the synthesis and characterization of SnP₂S₆ crystals with exceptional nonlinear optical properties and phase-matchability, supported by experimental and theoretical analysis.

Findings

Large non-resonant SHG coefficient of 53 pm/V at 1550 nm

Broad transparency range from 0.54 μm to 8.5 μm

High laser induced damage threshold of 350 GW/cm²

Abstract

High-power infrared laser systems with broadband 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 SnP_2S_6 with a large non-resonant SHG coefficient of d33= 53 pm/V at 1550nm and a large LIDT of 350 GW/cm^2 for femtosecond laser pulses. It also exhibits a broad transparency range from 0.54 {\mu}m to 8.5{\mu}m (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. A proximate double-resonance condition in the electronic band structure for both the fundamental and the SHG light is shown to enhance the non-resonant SHG response. Therefore, SnP2S6 is an outstanding candidate for infrared laser applications.