AMTIR-6 (As2S3)
Arsenic trisulfide glass (As2S3)
was first produced commercially in the 1950's. Because of the explosive
nature of sulfur reactions, the glass was prepared in an open system,
which led to large batch-to-batch variations in the refractive index and
related physical properties. In recent years, the open system has fallen
out of favor due to environmental considerations. Commercial sources
worldwide have ceased production.
During 1990, Amorphous Materials
developed a new closed process for making As2S3
glass. The process, containing several steps, uses element purification,
vapor phase reactions, glass compounding and glass purification steps to
cast a homogeneous plate 8" in diameter. The closed nature of the
process leads to tightly controlled quality.
Arsenic trisulfide glass has some very
unique properties. The light red glass transmits from the visible out to
8µm with no appreciable absorption. For systems operating in the near
infrared or the 3-5µm window, the glass is extremely useful for lenses
or windows. Generally, use in the 8-l2µm range is not recommended
because of intrinsic absorption.
Arsenic trisulfide glass has the lowest
thermal change in refractive index of any infrared optical material in
use today including germanium, AMTIR-l, AMTIR-3, zinc selenide and zinc
sulfide. For this reason, lenses or windows made from As 2S3
glass do not show optical distortion when subjected to the intense
IR radiation from lasers such as YAG, ER/YAG, or CO. The low thermal
change in refractive index is thought to be the basis for the fact that
700µm fibers made from As2S3 glass have been
reported to transmit more than 100 watts of laser energy from a CO laser
emitting at 5.4µm.
The glass is available in blanks up to 8"
in diameter or in slumped plates 12" x 18". As a melt-formed glass, As2S3
can be slumped or molded into most any shape or size. Also,
Amorphous Materials has developed a process to prepare optical fibers
from the glass in diameters ranging from 10-30 mils. The fibers are
glass clad/plastic coated or just plastic coated for sensor
applications. Lengths up to 100 meters can be obtained.
