Page 188 - Chalcogenide Glasses for Infrared Optics

164 Cha pte r Se v e n

14

12
Loss due to loop in fiber
Attenuation (arbitrary units) 8 6 3.4 4.6
10

4
3 6.1 6.4 Loss of fiber
6.8
2
8
0
2.5 4.5 6.5 8.5 10.5 12.5
Wavelength (µm)

FIGURE 7.7 FTIR measured absorption of AMI C2 fi ber straight and tightly coiled.

arsenic and sulfur. We could not use our normal plate process where
reactants are placed in the compounding chamber. The heat of reac-
tion between sulfur and arsenic is so great that the heat generated
would cause an explosion due to sulfur vapor. So we developed a
9
process in which, under vacuum, sulfur vapor was passed over
heated arsenic in a separate chamber to form As-S compounds that
were deposited in a third cool chamber as powders. The chamber was
sealed off under vacuum, and the powder was melted to form the
glass. The glass was removed and then processed in our normal plate
process. A cylinder of glass was removed from the plate and fiber was
drawn in our usual process. By this time AMI had acquired a Synrad
CO laser which emitted at 5.25 µm but only about 5 to 7 W. The energy
was easily transmitted by our As S fiber. The designation of the As S
2 3 2 3
glass fiber was changed to C2 fiber.
The As-Se-Te C1 glass fiber has low attenuation at 5.25 and 9.27 µm.
Even with the low absorption, fiber failure occurs at 5 W of laser
power. At 10.6 µm, failure occurs at lower power because of greater
absorption. Even glass cladding does not help. At that time, the
highest CO laser power at 10.6 µm was reported by Nishi et al. as
10
2
10 W, slightly better than the AMI experience. But cooling was used.
The AMI concluded that absorption was of course important but
∆N/∆T, the source of thermal lensing, was probably the most impor-
tant factor. The author had measured As S glass from room temperature
2 3
down previously and found a very low value, near zero. When it was