Page 245 - Chalcogenide Glasses for Infrared Optics

AMI Infrar ed Crystalline Materials 221

Refractive* Index at Absorption
Wavelength (mm) 25∞C Coefficient (cm )
-1
3 2.7026 < 0.01
4 2.6971 ”
5 2.6922 ”
6 2.6886 ”
7 2.6865 ”
8 2.6846 ”
9 2.6825 ”
10 2.6797 ”
11 2.6766 ”
12 2.6749 ”
∗ ν 3–5 µm = 163
† ν 8–12 µm = 173

Thermal Change in Index †
∆N/∆T × 10 /°C
−6
+147 @ 1.15 µm
+98 @ 3.39 µm
+98 @ 10.6 µm

∗ Melt formed crystal.
† R. J. Harris, Appl. Opt. 16, 436 (1970).

TABLE 9.2 Optical Properties of Cadmium Telluride

reach maximum transmission with no free carrier absorption. An
−1
absorption coefficient of 0.002 cm was measured at 10.6 µm by Laser
Power Optics. Table 9.2 lists the data found in the AMI product sheet
for melt-formed crystalline CdTe.

9.3.1 Conclusions
The AMI chalcogenide glass compounding process was modified by
adding a third chamber so plates of large-grain polycrystalline
cadmium telluride could be produced. Plates with as large as 10-in
diameter were tried, but failure of the quartz became a problem. Most
efforts were concentrated on using our regular 8-in chambers. The
slow freezing rate and the air-controlled directional freeze appear to
be a reliable method for producing relatively large volumes of
randomly oriented single-crystal regions. No single preferred growth
orientation was observed. In general, the plates were well com-
pounded, free of voids with very little, if any, dendritic growth.