11 July 1989 Calcium Fluoride: New Properties For An Old Material
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A new process for producing large, single, oriented crystals of calcium fluoride (CaF2) has been developed which overcomes the limitations of current growing methods. This process has been reduced to practice and has yielded oriented crystals 17.5 3 x 17.5 x 5 cm3. Currently nearing completion is a system for producing 35 x 35 x 7.5 cm3 single crystals. A scale up to one-meter-square is considered feasible. This crystal growing process makes possible the fabrication of very large CaF2 windows. Suitability for very high power lasers, however, requires attention to properties beyond mere size. A process to generate higher purity growth stock (starting material) was also developed. The additional purification of the growth stock contributes to lower bulk absorption, the absence of color centers and increased radiation hardness. Also identified were several specific impurities which correlate with radiation hardness. A correlation was found between color centers induced by laser radiation and ionizing radiation. The ability of the new process to produce oriented single crystals permits entire laser windows to be fabricated with the <111> direction parallel to the direction of propagation. This orientation is known to reduce thermo-optic distortion and stress induced birefringence. Other CaF2 crystal properties such as tensile strength, absorption and laser damage thresholds were studied and are discussed.
© (1989) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
C William King, C William King, Ontario H Nestor, Ontario H Nestor, } "Calcium Fluoride: New Properties For An Old Material", Proc. SPIE 1047, Mirrors and Windows for High Power/High Energy Laser Systems, (11 July 1989); doi: 10.1117/12.951353; https://doi.org/10.1117/12.951353


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