Optical design of inspection lens for internal defect of large-diameter chalcogenide glasses and experimental verification

Large diameter chalcogenide glasses play an important role in developing high resolution infrared imaging systems for various military and civil applications. However, it lacks an effective measure for inspecting the internal artifacts (including non-uniformity of refractive indices, impurities, and cracks) of bulk chalcogenide glasses and thus the application of such glasses was limited. A near infrared lens was developed for inspecting the internal artifacts of large diameter chalcogenide glasses. Considering the spectral characteristics of the chalcogenide glasses and a currently available infrared camera, the performance of the lens was optimized for the spectral band of 0.95-1.05 m. A group of three achromatic doublets was utilized to eliminate the chromatic aberration and realize an imaging performance that is close to a diffraction-limited system. Off-the-shelf glasses of K9 and F6 were used in this design. The proposed lens was tested in experimental settings for inspecting internal artifacts of chalcogenide glasses. According to the experimental results, the resolution of the proposed lens matches the design parameters well and many kinds of internal artifacts of chalcogenide glasses, including non-uniformity of refractive indices, impurities, and cracks, are clearly observed in images captured by the proposed lens.