Page 173 - Chalcogenide Glasses for Infrared Optics

Unconventional Lens Fabrication, Aspheric Surfaces, and Kinos 149

After Standard After Modified
Before Molding Molding
λ (µm) Molding Proc. ∆ Proc. ∆
3 2.7575 2.7622 +0.0047 2.7575 +0.0000
4 2.7530 2.7568 +0.0038 2.7523 −0.0007
5 2.7493 2.7534 +0.0041 2.7488 −0.0005
8 2.7426 2.7466 +0.0040 2.7421 −0.0005
10 2.7379 2.7418 +0.0039 2.7372 −0.0007

TABLE 6.3 Change in Index on Molding Amtir 5

four orientations on the mirror, left or right relative to the beam (L or R)
and up or down for the top of the prism (U or D). The four measure-
ments averaged lead to the accurate value, as has been demonstrated
a number of times for materials where the resulting values are com-
pared to those published by NBS or NIST.
To demonstrate the change in index on molding Amtir 5, we
have taken the before-and-after approach (Table 6.3). A prism was
fabricated from annealed glass from plate 04-23 and measured 3 to
10 µm in all four orientations. Next, glass from the plate was used
to mold a flat 5-in-diameter plate using our standard temperature
and pressure. A prism was fabricated from the plate and measured
in an identical manner. Then a second plate was molded at the
same temperature and pressure, only care was taken to release the
pressure at a point above the T in order to relax the compressed
g
liquid.
In conclusion, molding under pressure will increase the refractive
index appreciably, 0.0040. However, if the pressure is released before
the glass becomes a solid, the change is small, < 0.0010.
In summary, AMI has developed the technology to mold high-
5
quality lenses from glasses produced by AMI. Two low-softening
glasses developed were successfully used for molding. Antireflection
coatings were developed for these glasses. Lenses made using Amtir
4 and 5 are in several important military systems. AMI has applied
the knowledge learned to mold four of the seven glasses produced by
AMI shown in Table 6.4. Amtir 1 has not been molded because of its
high softening temperature of 405°C. Amtir 2 is a very likely candi-
date because of its similarity to Amtir 5. Amtir 4, not listed, is not
fully developed at this time. Amtir 4 is better than Amtir 1 in trans-
mitting visible light. The softening point of Amtir 4 is 277°C, well
over 100° lower than Amtir 1. Amtir 4 is a good candidate for mold-
ing. AMI has established production capability with five molding
production units.