Phase Matching Achieved by Bandgap Widening in Infrared Nonlinear Optical Materials [ABa3Cl2] [Ga5S10] (A= K, Rb, and Cs)

Abstract

Large nonlinear optical (NLO) coefficient (dij), high laser damage threshold (LDT), and phase matching (PM) are crucial for the practical applications of IR NLO crystals. A great number of IR NLO materials with high dij have been explored, but many of them suffer from non-PM, which dramatically decreases their ultimate NLO output efficiencies. To settle this problem, we have developed a new strategy involving modulating normal dispersion via bandgap (Eg) widening to achieve PM in this work. We synthesized successfully three new wide Eg (∼4.0 eV) IR NLO salt-inclusion sulfides [ABa3Cl2][Ga5S10] (A= K, 1; Rb, 2; and Cs, 3) with PM behaviors, mainly ascribed to the PM cut-off wavelength blue shift that originated from the wide Eg values, with less contribution from birefringence enhancement. All the compounds possessed large second-harmonic-generation (SHG) efficiency (∼1 × AgGaS2) and hitherto the highest LDTs (188–200 MW/cm2, at 1.06 μm, 10 ns pulse width) for known chalcogenides with SHG efficiencies comparable to that of commercial silver gallium sulfide (AgGaS2) crystal.