Raman gain and femtosecond laser induced damage of Ge-As-S chalcogenide glasses.

Chemical stoichiometric Ge-As-S glasses were prepared, and their thermal properties, refractive index (n), optical bandgap, Raman gain, and femtosecond laser damage were examined. Results revealed that the n and density (ρ) of the glasses decreased as Ge concentration increased, whereas the bandgap and glass transition temperature (Tg) increased. The Raman gain coefficients (g_R) of the samples were calculated on the basis of spontaneous Raman scattering spectra. g_R decreased from 2.79 × 10^-11 m/W for As₂S₃ to 1.06 × 10^-11 m/W for GeS₂ as Ge concentration increased. However, the smallest g_R was 100 times higher than that of fused silica (0.89 × 10^-13 m/W). When these glasses were irradiated by a laser with a pulse width of 150 fs and a power of 33 mW at 3 μm, the damaged area and depth decreased and the damage threshold increased gradually as Ge concentration increased. Raman spectra and composition analysis indicated that surface oxidation probably occurred and sulfur gasified at a high laser power. Although the g_R decreased as Ge was added, the laser damage threshold of Ge-As-S glasses was higher than that of the As₂S₃ glass. Thus, these glasses are potential materials for Raman gain media.