Thermal Lensing and Laser-Induced Damage in Special Pure Chalcogenide Ge35As10S55 and Ge20As22Se58 Glasses under Quasi-CW Fiber Laser Irradiation at 1908 nm

Special pure chalcogenide glass is the material of choice for many mid-infrared optical fibers and fiber lasers. In this paper, the thermo-optical lensing and laser-induced damage were studied in Ge35As10S55 and Ge20As22Se58 glasses and compared with the well-studied As2S3 glass. The thermal Z-scan technique with the quasi-CW Tm-doped fiber laser at 1908 nm was applied to study thermal lensing in chalcogenide glass. The laser-induced damage of various chalcogenide glasses was determined using the one-on-one procedure. The thermal nonlinear refractive index of the Ge35As10S55 and Ge20As22Se58 glasses was found to be lower than that of the As2S3 glass. The laser-induced damage threshold of the Ge20As22Se58 glass was determined to be higher than that of the Ge35As10S55 glass. The difference in the thermal damage threshold of the Ge35As10S55 and Ge20As22Se58 glasses and their lower value in comparison with the As2S3 glass were explained by a deviation from the stoichiometry of glass compositions and their tendency to crystallize.