Amorphous Materials began in 2000 a joint program with Lockheed Martin in Orlando to develop molding
technology required to produce infrared lenses from chalcogenide glasses. Preliminary results were
reported at this SPIE meeting by Amy Graham1 in 2003. The program ended in 2004. Since that time, AMI
has concentrated on improving results from two low softening glasses, Amtir 4&5. Both glasses have been
fully characterized and antireflection coatings have been developed for each. Lenses have been molded
from both glasses, from Amtir 6 and from C1 Core glass. A Zygo unit is used to evaluate the results of each
molded lens as a guide to improving the molding process. Expansion into a larger building has provided
room for five production molding units. Molded lens sizes have ranged from 8 mm to 136 mm in diameter.
Recent results will be presented
The development and use of arsenic trisulfide glass in infrared systems began in 1950. The glass was produced commercially in ton quantities by a number of companies in the US and Europe and used in NIR and MWIR systems mostly for commercial use. In the 60's, it became apparent that new optical materials capable of longer wavelength transmission would be needed for thermal imaging systems beginning to be considered. The government sponsored exploratory development programs aimed at providing selenium and tellurium containing glasses. By mid 1970's, two selenium based glass compositions had been developed and were in production in the U.S. Many tons of these two glasses have been produced and used in the 1980's, 1990's and present day for thermal imaging systems both military and commercial.
The fact that only two glass compositions have been used so extensively for such a long period is due in part to the size of the effort required to identify, characterize and produce a new glass to a state where it will be considered by the optical designer for use in new systems. But new compositions may be needed to provide a glass better suited for a different application. Glasses developed by Amorphous Materials for different applications will be described.
Efforts have resumed to improve the image quality of infrared imaging bundles formed at AMI using the ribbon stacking method. The C4 glass has been used to reduce core size, increase packing density and improve flexibility. Ribbons are formed from unclad fiber wound on a drum with pitch, ribbon count and spacing between ribbons computer controlled. A small portion of each ribbon is compressed and fused using thin, dilute Epoxy. Unfortunately, the Epoxy, serving as a clad, absorbs most all the LWIR energy making the bundles unsuited for 8-12 μm cameras. The ribbons are removed from the drum and stacked, one on top of the other observing proper orientation to form the bundle. A typical 1 meter bundle is formed from 50-70 count ribbons for a total of 2500-4900 fibers, made from 2.5-4.9 Km of C4 fiber. Typical core diameters are 60-80 μm. Active surface area ranges from 60-70%. Infrared resolution images formed using a NIR tube camera equipped with a special relay lens demonstrates the resolution limit for the bundle. Currently, the limit is about 10 lp/mm. The bundle end is imaged in the 3-5 μm Agema 210 camera using an Amtir 1 F/1 meniscus, coated 3-5 μm. Video images taken in natural light of an individual, easily recognizable at 50 feet, will be shown. Results of careful evaluation carried out at Lockheed Martin in Orlando using a high performance Raytheon Galileo camera will be presented.
With the advent of the uncooled detectors, the fraction of infrared (IR) imaging system cost due to lens elements has risen to the point where work was needed in the area of cost. Since these IR imaging systems often have tight packaging requirements which drive the optical elements to have complex surfaces, typical IR optical elements are costly to manufacture. The drive of our current optical material research is to lower the cost of the materials as well as the element fabrication for IR imaging systems. A low cost, moldable amorphous material, Amtir-4, has been developed and characterized. Ray Hilton Sr., Amorphous Materials Inc., Richard A. LeBlanc, Amy Graham and Others at Lockheed Martin Missiles and Fire Control Orlando (LMMFC-O) and James Johnson, General Electric Global Research Center (GE-GRC), along with others have been doing research for the past three years characterizing and designing IR imaging systems with this material. These IR imaging systems have been conventionally fabricated via diamond turning and techniques required to mold infrared optical elements have been developed with this new material, greatly reducing manufacturing costs. This paper will outline efforts thus far in incorporating this new material into prototype IR imaging systems.
Amorphous Materials has developed a chalcogenide glass which can be drawn in unclad fibers continuously with diameters as low as 50 micrometers . The glass, designed C4, was used to form bundles using the stacked ribbon method. The bundles, 1 meter long and containing 4 - 5 thousand fibers, fitted with relay and objective lenses, produced images using the 3 - 5 micrometers Agema 210 camera far superior than observed at Amorphous Materials with previous bundles. Resolution and contrast were markedly improved. Further improvement was observed when a bundle was used with a much more sensitive Raytheon Radiance it 3 - 5 micrometers camera. FTIR scans showed the transmission was low in the 8 - 12 micrometers range. Images obtained using a Raytheon Palm IR were faint with low contrast. Antireflection coating on the bundles improved 3 - 5 micrometers transmission but failed to improve the 8 - 12 micrometers performance sufficiently.
Efforts have been underway for several years at AMI to develop a ribbon stacking method to fabricate infrared imaging bundles from chalcogenide glass fibers. Bundles have been formed drawing fibers from an As-Se-Te glass (Cl) and from As2S3 glass (C2). Fiber core diameter has been limited to 100 ?m or greater due to the low tensile strength of chalcogenide glasses. Glass cladding adds strength to the fiber but results in low active area (25-35%) and coarse images. Use ofunclad fiber increases packing density ( active area 50-70%,) and improves infrared camera images. Recently, a new As-Se glass, designated C4, was developed at AMI, that can be drawn into flexible fibers with core diameters of 50-60 ?m. Bundles formed from stacked ribbons ofunclad fiber produce infrared camera images markedly improved over previous bundles. Imagery using C4 bundles made with small core unclad fibers and a Cl bundle made with glass clad 140 ?m core fibers, are compared. Images for both bundles made using a low sensitivity 3-5?m camera are compared to those made using a very sensitive 3-5 ?m radiometer camera.
Efforts have been underway for several years at AMI to develop methods to fabricate infrared imaging bundles from chalcogenide glass fibers. Bundles have been formed using fibers made from an As-Se-Te glass (C1) and from As2S3 glass (C2). Most have been made using 100 micrometer core fibers, clad and unclad. Bundles have contained as few as 100 active fibers and as many as 3000. Lengths have ranged from 1 to 10 meters. Methods of construction will be discussed. Evaluation results will be presented. Images formed using infrared cameras sensitive at 1.4 micrometer, 3 - 5 micrometer and 8 - 12 micrometer, will be shown.
Amorphous Materials (AMI) has been engaged for several years in developing a process suitable for forming coherent imaging bundles from small diameter chalcogenide glass fibers. Currently, in a SBIR II program funded by the Navy Air Warfare Center at Patuxent River, Md., efforts are directed towards forming a bundle 10 meters in length from arsenic trisulfide glass fibers using the stacked ribbon method. A drum 10 meters in circumference was constructed on which to wind the ribbons. The fiber core diameter goal is 50 micrometer. The bundle will be 7 mm square with an active fiber area greater than 50% and an overall transmission goal of 50%. Anti-reflection coatings on both ends are provided using the AMI coating facility. A unique method of forming imaging bundles will be discussed. Images formed during evaluation will be shown.
Amorphous Materials produces for IR applications three chalcogenide glass compositions: As2S3, Ge33As12Se55 designated AMTIR 1, and Ge28Sb12Se60 designated AMTIR 3. Methods of production will be discussed. AMTIR 1 and AMTIR 3 were used extensively in FLIR systems. Amorphous Materials produces thousands of small sensor lenses for non contact temperature measuring devices. Drawing of chalcogenide glass fibers at Amorphous Materials will be described. Chemical sensing is the main application. Currently, the fabrication of coherent fiber imaging bundles is under development. Extrusion of glass rods for chemical sensing will be mentioned.
Chalcogenide glasses have been produced commercially for use in infrared systems for almost 50 years. Only three glass compositions in the western world have been produced and used in ton quantities: As2S3, Ge33As12Se55, and Ge28Sb12Se60. Production of these three compositions at Amorphous Materials will be discussed. Physical properties of the glasses will be compared and related to the properties of other IR optical materials. Drawing of chalcogenide glass fibers at Amorphous Materials will be described.
At one time, arsenic trisulfide (As2S3) glass was the only IR optical material produced commercially for infrared optical systems. The glass was produced by the tons from the 50s into the 70s. However, as the emphasis shifted to the long wavelength 8 - 12 micrometer passive optical systems, the glass fell out of favor and production worldwide ceased. The production processes used were open systems which led to environmental concerns that also contributed to the decisions to cease production. In the 1990s, Amorphous Materials (AMI) became interested in the glass in part because of the reported ability of As2S3 glass fibers to transmit large amounts (greater than 100 watts) of laser power. A closed process which eliminated environmental concerns was developed to produce the glass. Major emphasis was in producing glass for IR fibers. Use for imaging systems was limited. Now, however, a trend has developed to produce imaging systems based on focal plane array technology which operate in the 3 - 5 micrometer wavelength region. A demand once again has been created for the glass. The method used at AMI to produce the glass is presented. Efforts to reduce absorption through purification of the elements are described. Properties of the glass are reviewed.
During the last 15 years, numerous programs have been carried out in the U.S., UK, France, Japan, Israel and Russia aimed at providing a flexible chalcogenide glass fiber suited for delivery of power from a carbon dioxide laser emitting at 10.6 micrometer. The success of these programs has been modest at best with output power limited to 10 watts or less. The purpose of this paper is to examine chalcogenide glasses used for fiber from a thermal lensing standpoint.
AMI is engaged in a number of programs to produce infrared transmitting fiber and lenses using AMTIRR materials, for commercial and military purposes. Through adaptation of Computer Engineering Services (author's prior company) conventional silicate glass extrusion technology, it is possible to fabricate fire polished rods and tubes of virtually any cross-sectional geometry. Diameters between about 3 mm and 75 mm and lengths as great as 1000 mm have been achieved. Extrusion is similar in many respects to fiber optic draw technology and requires precise control of feed and draw parameters, via the use of microprocessor systems. Internal homogeneity of the starting material is completely retained. This paper discusses the effort to date and describes product applications.
The results of attempts to fabricate coherent imaging IR glass fiber bundles have been described previously. The stacked ribbon method was used. The need to use smaller diameter fibers, more evenly packed was pointed out. Better methods to evaluate the optical performance of the bundle need to be developed. Results of continued efforts to improve are described.
Amorphous Materials has developed a unique method for preparing optical fibers from chalcogenide glasses. Fiber is drawn through a hole in the bottom of a heated, pressurized chamber containing a cylinder of a chalcogenide core glass. The fiber is passed through two heated split dies which apply a cladding glass and a plastic coating continuously. The fiber is pulled using a one meter drum equipped with accurate speed and pitch control. The method is ideally suited for the formation of IR glass ribbons which can be stacked upon one another to form coherent fiber bundles. Results of our first efforts are reported in this paper.
The use of chalcogenide non-oxide glasses as infrared optical materials began with the development of a commercial process to produce As2S3 glass around 1950. The volume production of FLIR systems in the 80s meant that such glasses were produced annually in `ton' quantities. Methods of production for the most commonly used glasses will be discussed. Optical and related physical properties; absorption, refractive index, thermal change in refractive index and optical homogeneity results for all passive IR materials used in FLIRS will be presented.
The advantages and disadvantages of several methods used to prepare gallium arsenide will be discussed relative to the preparation of large plates to be used as IR windows. Amorphous Materials chose to use the Horizontal Bridgman process to prepare plates 4 inch X 9 inch X 0.5 inch. Doped and undoped plates were prepared. Optical and electrical evaluation data will be presented. Scale up to larger sizes will be discussed. A unique process to protect gallium arsenide from rain erosion, provide EMI protection and de- icing capability will be described.
Amorphous Materials (AMI) has served since 1977 as a source of high purity, optically homogeneous plates of selenium-based glasses used in passive IR (FLIR) night vision systems. Over the past three years, Amorphous Materials has used this chalcogenide glass technology and capability to develop a unique process to prepare optical fibers. The process is based on using 2 inch cores removed from a homogeneous plate and sealed in a chamber which can be heated so that fibers may be pulled from a small tube in the bottom. Methods for cladding and coating with thermal plastic using split dies have been developed. The method has been used to produce flexible, low attenuation fibers based on an As-Se-Te composition. High purity As2S3 glass has been used to produce fibers capable of transmitting substantial amounts of IR laser energy. Physical properties of both fibers are discussed.
The precise infrared refractive index for polycrystal and single crystal germanium was measured using the prism minimum deviation method. Samples were obtained from three major suppliers. Values for single and poly are compared. Variation among suppliers is discussed.
Amorphous Materials serves as a source of high purity IR transmitting chalcogenide glasses. Based primarily on the element selenium, the glasses are used for optical elements in passive IR optical systems. However, because of their transparency in the IR combined with chemical inertness, the glasses can be used to fabricate ATR plates for chemical analysis. Addition of the element tellurium extends the long wavelength transparency of selenium glasses increasing their suitability for use as IR fiber materials. Uncoated fibers may be used in the same manner as ATR plates for chemical analysis. Production of glass and fibers are discussed.
The precise (five number) infrared refractive index of AMTIR-I
glass and chemical vapor deposited zinc selenide were measured
over the wavelength range 3-l2pm. The results were temperature
corrected and compared to standard values.
Chalcogenide glasses of the systems Ge-Sn-Se, Ge-Se-Te and Ge-Sn-Se-Te have been prepared. The
region of high IR transparency of Ge-Se-Sn, Ge-Se-Te and Ge-Sn-Se-Te glasses was slightly expanded
(1 -2 m) towards longer wavelengths, compared to Ge-Se glasses. The intensity of the impurity absorption
peak of Ge-O (at A 12.8 pm) which usually appears in Ge-Se glasses, was reduced or absent in Ge-Sn-
Se-Te glasses. The expansion of IR transparency and the reduction of Ge-O absorption peak enable one to
employ these glasses for drawing fibers for CO2 laser radiation (10.6 jim) transmission.