Modified Bridgman Technique Growth of Cadmium Telluride for High Power Infrared Laser Windows.
Final technical rept. 15 Jun 71-30 Jul 72,
HUGHES RESEARCH LABS MALIBU CA
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This program was undertaken to study the feasibility of CdTe for use as a high-power infrared laser window. Although the study began with single crystal CdTe, the mechanical properties of the material indicated that a significant gain in yield strength could be achieved with a polycrystalline body with no apparent loss in optical absorption at 10.6 micrometers. This investigation involved preparation of polycrystalline CdTe as 5 cm diameter ingots by the Modified Bridgman Technique. During the course of this program, polycrystal ingots were grown weighing nearly 1 kilogram. The modulus of rupture of single crystal CdTe was found to be in excess of 3000 psi, a value much larger than reported up to that time in the literature. A thermal annealing process was established which reproducibly yields low absorption material and is applicable to ingots grown under a variety of conditions. The study led to the fabrication of 5 cm diameter CdTe disks having measured absorption coefficients as low as 0.00089cm and typically less than 0.002cm. It is concluded that CdTe is feasible for application as a high power infrared laser window because of its low optical absorption and demonstrated strength in polycrystalline form. A significant step in proving feasibility is the development of the thermal annealing process which holds the possibility of further improvement in 10.6 micrometers transmission by allowing a lowering or elimination of dopant concentration thus decreasing defect concentration and the probability of precipitate formation.
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