Giant Non-resonant Infrared Second Order Nonlinearity in $\gamma$-NaAsSe$_2$

TL;DR

This paper reports the growth of $ ext{NaAsSe}_2$ crystals with giant non-resonant infrared second-order nonlinearity, combining high NLO coefficients, suitable bandgap, and broad transparency, ideal for infrared laser applications.

Contribution

The study introduces $ ext{NaAsSe}_2$ as a new NLO crystal with unprecedented second harmonic generation susceptibility and phase-matching capabilities.

Findings

Giant SHG susceptibility of 590 pm V$^{-1}$ at 2μm

Similar bandgap (~1.87 eV) to existing materials

Transparency range up to 16μm

Abstract

Infrared laser systems are vital for applications in spectroscopy, communications, and biomedical devices, where infrared nonlinear optical (NLO) crystals are required for broadband frequency down-conversion. Such crystals need to have high non-resonant NLO coefficients, a large bandgap, low absorption coefficient, phase-matchability among other competing demands, e.g., a larger bandgap leads to smaller NLO coefficients. Here, we report the successful growth of single crystals of $\gamma$-NaAsSe$_2$ that exhibit a giant second harmonic generation (SHG) susceptibility of d$_{11}$=590 pm V$^{-1}$ at 2$\mu$m wavelength; this is ~ eighteen times larger than that of commercial AgGaSe$_2$ while retaining a similar bandgap of ~1.87eV, making it an outstanding candidate for quasi-phase-matched devices utilizing d$_{11}$. In addition, $\gamma$-NaAsSe$_2$ is both Type I and Type II phase-matchable, and has a transparency range up to 16$\mu$m wavelength. Thus $\gamma$-NaAsSe2 is a promising bulk NLO crystal for infrared laser applications.