Optical loss and residual stress measurement of infrared chalcogenide glasses and analysis on its influencing factors

Chalcogenide glasses (ChGs) have a relatively small temperature coefficient of refractive index, broad transmission range from almost visible to mid-infrared. It is suitable for precision molding. With the help of above mentioned merits, ChGs have a vast reservoir of value in the field of military and civilian infrared imaging. However, the internal defects of ChGs are caused by melting, cool-demoulding and annealing in a high vacuumed ampoule. The defects include the optical inhomogeneity, chemical inhomogeneity and built-in stress which trouble the homogeneity of ChGs and directly affect the imaging quality of infrared imaging devices. The detection and control of internal defects is a key technique. In this paper the platform for testing, characterization and evaluation of the inhomogeneity of ChGs will be designed and built. The appropriate testing and evaluation criteria of inhomogeneity during the preparation procedure of ChGs in the vacuumed ampoule will be studied. The transmittance of ChGs sample is measured repeatedly. The factor of internal multple reflection in ChGs sample is analysed and discussed. Analysis shows that the mean transmissivity of ChGs sample (Ge28Sb12Se60) with thick of 1 cm is approximately 66% in 8 to 11 microns. The loss is less than 2.40%/cm. The optical path difference (OPD) caused by residual stress in ChGs sample is less than 5.2 nm/cm. The results will provide a technical support to optimize the ChGs preparation process and improve the ChGs homogeneity.