Two phases of Ga2S3: promising infrared second-order nonlinear optical materials with very high laser induced damage thresholds

Abstract

Two phases of Ga₂S₃ with different space groups Cc and F3m were synthesized in pure phase by a facile boron–sulfur–metallic oxide reaction. They both have a good transparency in the wavelength range of 0.44–25 μm and exhibit comparatively large second-harmonic generation (SHG) effects of about 0.7 and 0.5 times that of commercial KTiOPO₄ (KTP), for the monoclinic and cubic Ga₂S₃ respectively. The monoclinic Ga₂S₃ is phase-matchable at the wavelength of 1910 nm while the cubic phase is non-phase-matchable. In order to study their powder laser induced damage threshold (LIDT) properties, a single pulse powder LIDT measurement method was proposed and it was found that they have very high powder LIDTs of about 30 and 100 times that of AgGaS₂ (AGS), respectively for the monoclinic and cubic phase, under a single pulse 1064 nm laser radiation with a pulse width τ_p of 8 ns. To gain further insights into the nonlinear optical (NLO) and LIDT properties of the monoclinic and cubic Ga₂S₃, calculations of second-order NLO susceptibility and lattice energy density (LED) were also performed to explain their SHG efficiencies and high LIDTs.