This paper describes a novel technique to visualize, 'in situ,' the solid-liquid interface during directional solidification. It is based on the principle of 'Infrared Autoradiography.' This technique is in general applicable to infrared materials depending upon their infrared transmission range and availability of infrared detection/imaging system in that range. Preliminary results on the application of this technique to potassium chloride (KC1) are included. The technique will allow, for the first time, 'in situ' monitor and control of interface shape and thus, help grow better quality crystals. In addition to the improvement in the crystal quality, the technique will have wide range of fundamental and practical applications in solidification processes of advanced IR materials.
A monolithic Midwave InfraRed (MIR) sensitive array based on PbTe photoconductive sensors and a silicon CCD current integrator and multiplexer is manufactured and evaluated.. The dark current of the devices can be kept sufficiently low to allow for integration times of 4.4 msec. The responsivity and the detectivity D* of the device are quite high and can be compared to other types of IR sensors for the same wavelength range. The responsivity uniformity of the PbTeCCD is better than 10 %.
The new (HgZn)Te alloys were found to present numerous advantages over (HgCd)Te, such as increased stability of the crystal lattice and reduced dislocation density. A suitable growth process is already in place. Adaptation of the classical (HgCd)Te planar process technology (ion implantation instead of mercury diffusion) permits the duplication of the performance characteristics found in (HgCd)Te. A particular attribute of this material is its exceptional performance at very long wavelengths and its stability at elevated temperatures. With growth method and process technology already in existence, series fabrication of these devices can be implemented without major problems. In view of the numerous technical advantages offered by (HgZn)Te over (HgCd)Te detectors, these may be considered to be serious candidates for future infrared systems.
Schottky barrier diodes have received much attention for use as detectors in fiber optic communication systems requiring large bandwidth and good signal-to-noise performance. This paper will discuss what characteristics go into making maximum performance avalanche Schottky barrier detectors and why the Schottky barrier diode is a good candidate. Specifically, the report will discuss the design and performance of platinum silicide (PtSi) Schottky diodes.
A research program was undertaken to determine the surface figure error of several different types of mirrors at cryogenic temperatures. Two-inch diameter parabolic, spherical and flat mirrors were fabricated from zerodur, aluminum and a metal matrix composite of silicon carbide reinforced alumi-num (SXA). The ratio of silicon carbide to aluminum was selected so that the cofficient of thermal expansion (CTE) of the metal matrix matched electroless nickel. A liquid helium dewar was modified to add an interferometric grade window, a cold electronic shutter and a strain-free copper mirror mount. Interferometric phase measurements on each mirror mounted in the dewar were made without the window, with the window, under vacuum, at around 80K and between 10K and 24K.
Oxygen-free copper mirrors are currently used for transmitting, aiming and focusing high power infrared laser beams. When used in automated laser material processing systems, additional requirements are demanded of them. This paper deals with the solution adopted for their design, manufacture, assembly and in-service testing, as applied to laser welding heavy section components in AISI 304 with a 15 kW CW carbon-dioxide laser. The beam handling devices were used to demonstrate the suitability of the laser welding technique for assembling some of the structures of the reactor core in the French Superphenix nuclear plant. Two multiple rotating mirror systems, connected to each other for correct processing, had to be manufactured to perform circular welds to join sleeves to the plates of tne main diagrid, with a welding thickness of up to 15 mm. AISI 304 stainless steel is suitable for defect-free laser welded joints. Each multiple mirror systeid was dedicated to a particular welding technique: the first with the laser impinging uwards on the workpiece, the second downwards. In the latter case, special assist gas nozzles were needed to protect the mirrors from the metal vapour jets. Beam handling on a horizontal plane was also tested using another rotating mirror system for internally welding sleeves to plates. The results demonstrated the feasibility and suitability of the automated process for industrial applications. The accuracy of the results obtained using the multiple mirror system enables it to be adopted for assembling metallic structures similar to the Superphenix main diagrid. The reduction in manufacturing costs using such automated laser beam handling devices is calculated to be 30 - 40% of the total.
The emission spectra of Nd3+13"alumina and Eu313"alumina are reported. Consideration of the effect of site symmetry upon the intensity and lifetimes of the emission peaks leads to assignment of the exchanged ions to mid-Oxygen sites in the 13"alumina crystals.
Lanthana-strengthened yttria is of interest for infrared applications because of its high strength, long wavel-ength cutoff (8 μm), and low emissivity. The optical, thermal, and mechanical properties of the family of La203-strengthened Y203 have been characterized. The properties can be tailored to suit the requirements of specific applications by adjusting composition and processing parameters. The La203 acts as both a densification aid during fabrication and an agent for microstructural control. Since both strength and toughness depend on microstructure, the La203 allows significant strength enhancement, an important factor for window applications. Theoretical parameters have also been calculated to aid in the assessment of relative resistance to thermal shock fracture initiation. and propagation. These calculations reveal potential inconsistencies that must be resolved by experimental testing.
Calcium lanthanum sulfide (CLS) is under development as a long wavelength infrared (LWIR) window/dome. A coating has been demonstrated to protect CLS from the effects of high humidity and to increase its resistance to rain drop impact damage. Coated CLS exhibits better impact damage resistance than coated ZnS. Processing studies have focussed on improving the optical quality and fracture strength of CLS. Recent work has also concentrated on materials with a molar composition of 90 La2S3 : 10 CaS.
Various semiconductors were evaluated for use as infrared optical materials. The materials evaluated include gallium arsenide, gallium phosphide, germanium, silicon, zinc sulfide and diamond. The method used to produce the materials is reviewed. Semi-insulating polycrystalline gallium arsenide was produced by a horizontal Bridgman process to sizes of 8 by 12 by 0.7 inches. Gallium phosphide was produced by a liquid encapsulated Czochralski technique to 2-inch diameter and 3-inch length. Germanium was obtained commercially from a casting technique. High-resistivity silicon having a 1-inch diameter and 6-inch length was obtained from a float-zone process. Zinc sulfide was obtained commercially from a chemical vapor deposition process. Polycrystalline diamond was obtained by a microwave chemical vapor deposition process. The optical, electrical, mechanical, and thermal properties of these materials are presented and compared. Thermal shock, rain erosion, and modulation transfer function analyses were performed, and the results for each material are presented and compared. It was found that all these materials have useful physical properties as infrared optical components in a wide range of applications.
Measurements have been made of the IR transmission of several materials at temperatures up to 600°C. The materials measured in the study represent some of the most commonly considered materials for airborne FLIR (forward looking infra-red) sensor windows and missile domes in both the 3-5 micron and 8-12 micron wavebands. All materials show a reduction in overall IR transmission when heated. The general effect is an extension of the phonon absorption band to shorter wavelengths so reducing the waveband over which the material transmits.
Current applications of optical window materials require a compre-hensive characterization of the index of refraction and absorption coefficient as a function of frequency and temperature. General models of multiphonon absorption and one-phonon resonances are used to characterize the complex index of refraction of polar crystals. Experimental data from 100 to 5000 cm -1 at a variety of temperatures are used to determine physically meaningful parameters in the models. Extrapola-tions outside the experimental range of temperature and frequencies are valid. Thus, the model is of great utility. A review of the theory used in this model is given. Results of the application of the model to oxides, fluorides, and alkali halides are also presented. The absorption coefficient from 105 to 10 -5 cm -1 and the index of refraction from radio frequency to visible are obtained.
This investigation will examine differences in the diamond machined surface structure of various mono and polycrystalline germanium material forms. Germanium substrates were machined under controlled conditions and evaluated for surface texture and subsurface damage. Results of the substrate evaluations along with details of the sample preparations and machining are given.
Although heavy metal fluoride (HMF) glasses potentially offer high intrinsic transparency in the infrared spectral region, losses associated with extrinsic impurity absorption and scattering presently limit their uses in practical applications. This paper focuses on the design of an environmental control chamber and draw facility for minimizing water and oxygen contamination during the drawing of fluoride glass optical fiber. A vertical glove box arrangement of novel design encloses the draw tower area in which the preform and bare optical fiber are susceptible to moisture and water absorption. This area includes the preform chuck, the draw furnace, the fiber diameter monitor, the fiber coating equipment, and diagnostic instrumentation for measuring fiber tension and temperature. Plans for evaluation of various drawing techniques including rf/preform, resistance/preform, and rf/crucible are described, along with fiber coating techniques including oxide and non-oxide glass overcladding and UV-curable polymers.
Fluoride glass optical waveguides (ZBLAN) were coupled to a Fourier Transform Infrared Analyzer (FTIR) to execute remote IR chemical sensing. These fibers were used passively for only signal transmission, and the sensing was accomplished by direct or evanescent absorption of the fundamental modes corresponding to the desired chemical species. Due to the poor chemical and physical durability of fluoride glass, a crystal optrode (ZnSe) was used for evanescent wave absorption to isolate the fibers from the sensing environment. Several different types of chemical mixtures were studied to show the flexibility and limitations of such a system: 1) methane gas concentration in nitrogen using the C-H absorption at 3.31 um, 2) alcohol concentration in water using the C-H absorption at 3.36 um, and 3) water concentration in 1,4 dioxane using the 0-H fundamental stretching mode at 2.9 um. The last mixture proved to be the most difficult to analyze due to the low transmission of the fluoride fiber system in the 2.9 um region.
Applications such as laser microsurgery and coronary angioplasty require precise removal of tissue without thermal narcrosis. This necessitates using a wavelength which is strongly absorbed by the tissue and is fiber deliverable. Although silica glass fibers can deliver the visible argon and near infrared Nd:Yag laser beam, these wavelengths are poorly absorbed by tissue and precise tissue removal is impossible due to the large penetration depth. The 10.6 micron wavelength of the CO2 laser is highly absorbed by tissue, but fiber delivery is not possible especially because of the high peak power pulses necessary to eliminate charring. The ultraviolet excimer laser beam can precisely cut tissue, but fiber delivery is difficult, the radiation may be mutagenic, and the laser is large and difficult to adapt to the clinical setting since toxic halogen gases are used.
This paper describes the preparation and characterization of chalcogenide fibers for applications such as imaging and remote optical powering. The fibers were drawn from rod preforms and clad with a UV-cured urethane acrylate coating. The polymer clad fibers were 250 gm in diameter. Extended lengths up to 0.5 km of fiber were achieved that exhibited excellent strength and flexibility.
Hollow fibers are regarded as potential waveguides for radiation from C02-Lasers. We report on conditions for hollow fibers capable of delivering high-power radiation 100 W). We consider fibers with an air-filled core and a massive uncoated cladding. Technical requirements concerning the transmittance, numerical aperture, bending radius, and thermal effects lead to conditions for the refractive and absorption indices of the cladding material. Until now no oxide glass is known that is suitable for hollow fibers transmitting high-power radiation in the mid-infrared region. Further investigations were done with the parameters of crystalline, metallic and semiconducting materials. However, these materials do not fulfil the requirements of high-power hollow fibers either.
The intense polarized Raman Zr-F stretching frequency, √s, was examined for fluorozirconate glasses having stoichiometric F/Zr ratios from =4.6 to 8.0. This frequency was observed to decrease at a decreasing rate, from 605Ã‚Â±10 cm-1 (at F/Zr = 4.64) to 560Ã‚Â±10 cm-1 (at F/Zr = 8), and finally to =555 cm-1 (melt, at F/Zr = 10). This decrease suggests the presence of a succession of complex anions, e.g., ZrF5-, ZrF62-, and ZrF73-, as well as ZrFs4-, and possibly the neutral species ZrF4. A decrease in the symmetric Zr-F stretching force constants resulting from increasing Zr-F distances is thought to explain the observed nonlinear decrease in the I√s frequency.
A review of the preparation, characterization and properties of aluminate glasses is presented. The review begins with a discussion of the theory of glass formation and its application to aluminate glasses, and continues with a listing of glass-forming aluminate compositions. It concludes with an overview of the optical properties of these glasses, especially infra-red transmission. A few remarks are offered regarding potential research and application of these glasses.