Page 108 - Chalcogenide Glasses for Infrared Optics

86 Cha pte r T h ree

FIGURE 3.14 Striae scope photograph looking through an 8-in-diameter
striae-free Amtir glass plate.

round chamber thoroughly. The glass is cooled to slightly above T ,
g
the furnace is opened, and air is blown on the chamber to quench the
glass. After cooling, the quartz chamber is broken and the glass plate
is removed. The plate undergoes a preliminary evaluation and then is
placed in an oven to go through its anneal cycle. After annealing, the
glass is ready for processing by sawing, core drilling, or slumping
into shapes required for blanks to be fabricated into optical elements
used in imaging systems.
The AMI closed compounding casting glass process has produced
from 1978 to 2007 over 35 tons of Amtir 1 glass in 9-kg plates. Figure 3.14
shows a striae scope photograph taken looking through an 8-in-
diameter striae-free plate of Amtir glass.

3.6 Summary

1. High-purity elements are required to produce low-absorption
infrared chalcogenide glasses. The elements used are by-products
from the production of primary metals.
2. Glass may be made in kilogram quantities in simple tubes
placed in a rocking furnace. Optical quality will not be good.
3. Early TI casting units were open with melted glass poured from
a crucible into a mold. Again, optical quality was not good.
4. Quality improved at TI when the glass was allowed to flow
through a tube in the bottom of the crucible into a mold
below.