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

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 τp 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.