Page 182 - Chalcogenide Glasses for Infrared Optics

158 Cha pte r Se v e n

volatile selenium was distilled and remained in the lower-temperature
chambers 3 and 4. The first half fraction had much higher absorption.
The fourth chamber was high in S and Si which may account for the
large absorption. The second half was less volatile and at higher tem-
peratures remained in chambers 1 and 2. The second half fraction had
absorption at 10.6 µm less than one-third of the more volatile frac-
tion. Chambers 1 and 2 had by far the lowest levels of S and Si. The
analytical results for beginning Asarco powder show much higher
levels of S and Si. These results indicate these two impurities S and Si
are major contributors to the absorption value at 10.6 µm but may be
lowered in concentration by distillation of selenium.
AMI supplied glass in billets to Codman so that they could be
extruded into rod form. The rods were then drawn into fiber and
tested. Also AMI developed methods to cast rods in quartz tubing.
There was difficulty in removing the glass from the tubes. We started
precoating the tubes with a carbon film before the glass was added.
In retrospect, this was not a good idea because hydrogen selenide
forms when selenium reacts with carbon. AMI also produced rods by
sawing square pieces from flat plates. The square rods were then
ground round. Methods were developed to spin-cast thin-walled
cylinders in sealed evacuated tubes containing the clad glass. The
rods were then placed in the tubes, and the tubes collapsed and sealed
to the rod using gentle heat to form a core-clad preform.
Efforts to meet the Codman goals concentrated on improved
quartz fabrication techniques, use of high-purity selenium, and good-
quality rod preform fabrication. AMI reached the Codman goals and
concluded the research agreement in December 1985. Evaluation
results of the glass from Codman (Tom Loretz, John Smith, and Gino
Lombardo) agreed. Good fiber was produced. Transmission of 15 W
6
of CO laser power through the fiber was reported at SPIE as part of
2
an AMI paper. Glass and preforms continued to be produced and
used by Codman. Unfortunately, as time passed, it became apparent
that glass produced by AMI and used by Codman later in 1986 was
not of constant quality. Purchase of glass by Codman declined and
did not reach the amount specified in the agreement. For this and
other reasons, the Codman program ended in 1986.

7.2 AMI Fiber Drawing Process
Until late in 1986, AMI was convinced that we had achieved our
goals. As we became aware of fiber results at Codman, Galileo Electro-
Optics, and Infrared Fiber Systems, we realized our joint efforts had
not been very successful. The combination of our methods and theirs
was not producing good results. We decided in 1987 to investigate
and identify the problems related to our glass producing poor fiber
results. The first step was to purchase a carbon dioxide laser. We took