Low Loss Window Materials for Chemical and CO Lasers,
AIR FORCE CAMBRIDGE RESEARCH LABS HANSCOM AFB MASS
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The optical absorption has been measured in a variety of materials such as fluorides and titanates, which are candidates for service as low loss windows on DF-HF chemical or CO lasers. Measurements of the absorption coefficient beta at DF 3.8 micrometers and HF 2.7 micrometers frequencies were accomplished using cw chemical laser calorimetry. Beta as a function of frequency was obtained for the alkaline earth fluorides by measuring the spectral emittance at 100C. A phenomenological model has been employed to calculate beta for these hosts as a function of frequency. Good agreement is obtained between theory and experiment. The calorimetric results indicate that the absorption in most materials studied is limited by extrinsic processes. At HF frequencies, hydroxyl ions in the bulk or on the surface are believed responsible for the high beta values. At both DF and HF frequencies surface absorption appears to be strong owing in part to absorption by organics which are often used in surface finishing.
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