OPTICAL
A large variety of thin films
have been designed and developed with requirements that address many
different applications. The films below are representative of
some of the films that have been produced. Click on the desired(
)
to navigate.
AR()
BEAMSPLITTER()
POLARIZERS()
TELECOM()
EYE PROTECTION()
A variety of processes were used to produce the thin films. Some of these processes are discussed and illustrated below.
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A requirement existed for an anti-reflection coating to operate over a 40 NM bandwidth at 1550 NM and 45 degrees angle of incidence. It was desired that both the "p" and the "s" polarization components reflect less than 0.25%. This was a very difficult coating that required approximately 12 layers, each with a different thickness to achieve the theoretical performance. Successful deposition demanded thorough knowledge of the material properties and the chamber characteristics. The theoretical performance is illustrated in a chart that can be viewed by clicking on the chart icon.
This coating was a 50 % beamsplitter coating for "p" polarization at 364 NM. It was required that the coating be able to maintain this spectral performance after being subjected to intense laser radiation for several hundred hours. The coating was applied to one half of a parallel plate and was used in an optical assembly that produced 32 output beams from one input beam. The allowed intensity variation in the 32 beams restricted the 50 % tolerance to a band approximately 0.5% wide at 50%. The 32 beam assembly is further described on the engineering page.
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POLARIZERS:
A variety of polarizing coatings have been designed and developed to operate at wavelengths from the UV(~250 NM) to the near IR(~1060 NM). Polarization bandwidths have ranged from several nanometers to a couple hundred nanometers. Extinction ratios have ranged from approximately 100:1 to 1000:1. The spectral performance of a UV polarizer can be viewed by clicking on the chart below.
A variety of coatings were designed and developed for the telecommunications industry. This included coatings for application to air spaced and solid etalons, and DWDM filters. The etalon coatings were produced with an ion assisted process while the DWDM filters were produced with an ion beam sputtering process. The spectral characteristics of a typical 100 GHz DWDM filter can be seen by clicking on the chart button.
The increasing presence of lasers on the battlefield gave rise to a need for an optical coating that could provide eye safety with minimum impact on vision. There were primarily three wavelengths that were of concern. It was critical for the coated parts to block all wavelengths simultaneously while maintaining as high a photopic transmission as possible. Filters that performed to these standards were designed and developed for protection of both the human eye and military hardware. The spectral graph of a filter that was developed for eye protection can be viewed by clicking on the chart button below.
A variety of processes have
been used to deposit the coatings described above. This has included
plasma enhanced chemical vapor deposition processes (PECVD), RF
sputtering, ion beam sputtering, reactive ion beam sputtering,
reactive ion assisted evaporation, and traditional e-beam
evaporation. During the course of coating development
deposition models were frequently created to guide changes that were
made to the configuration of the e-guns or the planetary systems in
the chambers. The chambers used were implemented as required with
transmission, reflection, or qcm monitors to measure the deposition
thickness while it was being applied. They were also
frequently equipped with ion sources or other plasma generators to
provide in-situ cleaning or densification of the thin film.
Shown in the pictures()
from the left to the right are 1) a large (54 inch diameter) coating
machine that was used to produce laser eye protection filters,
2) The center machine was manufactured as a 30 inch automatic
box coater that was ultimately implemented with advance sweep
controls and an ion source, 3) The chamber on the right is a PECVD
machine that was initially used to coat hard carbon on germanium but
was subsequently modified to coat hard carbon on IR windows
fabricated from Tuftran ( a Zns/ZnSe composite).