Quality control of infrared optical elements fabricated from visually opaque materials can be accomplished either during manufacture or after completion by the use of the Evaporograph, a thermal-imaging device. The wavelength range for which the components are designed is used for this inspection. Localized variations in transmittance ranging from 100% to less than 1% are detected and typical examples are shown. The same technique can be applied to the inspection of antireflection coatings. The results obtained are enhanced by the use of suitable filters and examples are shown. Other applications include the inspection of images produced by infrared optical systems, and the determination of birefringence.
Gene W. McDaniel and Arthur P. DiMattia, "Inspecting Infrared Optical Materials and Systems by Means of the Evaporograph," Appl. Opt. 1, 483-491 (1962)