Precision glass molding has a well-documented decrease in the index of refraction of the glass during the molding process. This index drop must be taken into account in the optical design in order to accurately determine the optical performance of the final lens. Knowing the annealing coefficient of the glass being molded allows the index to be fine-tuned by adjusting the cooling rate during the molding process. While annealing coefficients are available for visible glasses, the validity of using this method for chalcogenide gasses has not yet been investigated. This paper will determine the annealing coefficient for As40Se60 experimentally, and then verify the results by comparing calculated and experimental refractive index values for other cooling rates.
The growing demand for thermal imaging sensors and cameras has focused attention on the need for larger volumes of lower cost optics in this infrared region. A major component of the cost of thermal imaging lenses is the germanium content. As40Se60 was developed as a moldable, germanium-free chalcogenide glass that can serve as a low cost alternative to germanium and other infrared materials. This material also has promising characteristics for improved optical performance, especially with regard to reduced thermal sensitivity. As40Se60 has found acceptance as a material to be diamond turned or polished, but it is only now emerging as a legitimate candidate for precision glass molding. This paper will review chalcogenide molding and characterize As40Se60 for widespread use in highvolume thermal imaging optics. The relative advantages and disadvantages of As40Se60 as compared to other chalcogenide glasses will also be discussed.
Precision glass molding has a well-documented effect of a decrease in the index of refraction of the glass during the molding process. This index drop has such significant value that optical designs for molded lenses must take into account the index drop to accurately determine the optical performance of the final lens. Widespread adoption of chalcogenide glasses for molded infrared optics has raised a series of questions as to the behavior of these glasses under molding conditions. This paper will investigate the index of refraction changes in two different chalcogenide glasses and determine if these changes are significant enough for optical designers to consider in their designs.
The growing demand for lower cost infrared sensors and cameras has focused attention on the need for low cost optics
for the long wave and mid-wave infrared region. The combination of chalcogenide glasses and Precision Glass Molding
(PGM) is the enabling technology for low cost infrared optics. The lack of detailed material properties data has limited
its acceptance in the commercial market, but increased demand and recent cost reductions in infrared sensors has
focused additional attention onto these materials as a cost driver for infrared systems. This investigation reviews the material performance and repeatability for a number of different chalcogenide glasses. Material properties including composition, glass transition temperature (Tg), coefficient of thermal expansion (CTE), index of refraction, transmission and change in index over temperature (dn/dT) are explored. Specific attention is given toward glasses that achieve high yields during precision glass molding and are candidates for commercial success.