DIFFRACTIVE INFRARED OPTICAL-ELEMENTS IN CHALCOGENIDE GLASSES

Aspects of the fabrication and performance of infrared diffractive opt ical elements based on the metal-photodissolution effect in As-S glass es are investigated. It is shown that the exposure time required to pr oduce such elements can be decreased by an order of magnitude by heati ng the As-S/Ag film combination to similar to 110 degrees C during ill umination. Bulk phase gratings made using this effect were found to ha ve good stability at elevated temperatures: trial gratings held at 100 degrees C in the dark for over 6 months did not deteriorate significa ntly, although the Ag continued to diffuse thermally into the undoped regions. The results of a theoretical analysis based on numerical solu tion of the appropriate coupled-wave equations predict that > 95% effi ciency should be possible with suitable anti-reflection coatings and o ptimised structures.