Special Section Commemorating the 50th Anniversary of the Laser

High-energy laser windows: case of fused silica

[+] Author Affiliations
Claude A. Klein

c.a.k. analytics, int’l, Nine Churchill Lane, Lexington, Massachusetts 02421

Opt. Eng. 49(9), 091006 (September 13, 2010). doi:10.1117/1.3484946
History: Received November 25, 2009; Revised June 07, 2010; Accepted June 28, 2010; Published September 13, 2010; Online September 13, 2010
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The engineering of high-energy lasers for applications such as the AirBorne Laser (ABL) system requires optical windows capable of handling megajoule pulse energies. The selection and/or evaluation of a suitable window material involves considerations relating to thermal lensing, i.e., the beam distortion caused by thermally induced phase aberrations, in addition to issues arising from the thermal stresses generated by beam-induced temperature gradients. We document analytical methods for evaluating the impact of beam-induced optical distortions and beam-induced mechanical stresses, which may enable the designer to properly assess the performance of window-material candidates. We illustrate the procedure in the light of an evaluation of the performance of the leading candidate for operation in the near-infrared, i.e., fused silica (SiO2). In terms of allowable peak intensities, and based on available material properties, the limiting factor is seen to be related to shear stresses generated by coating-induced axial compression that may lead to plastic deformation. The allowable beam fluence is controlled by thermally induced phase distortions rather than planar or axial stresses, thus reflecting the unusually small αEχ ratio of fused SiO2, where αE represents the thermal stress factor, and χ designates the optical distortion coefficient. In conjunction with an evaluation of the required window thickness as a function of the diameter, our analysis leads to the conclusion that operating the ABL system at the projected power level (2MW) and pulse duration (5s) requires bulk windows—if made of fused SiO2—of at least 20cm in diameter but no more than 7.5mm in thickness.

Figures in this Article
© 2010 Society of Photo-Optical Instrumentation Engineers

Topics

Lasers ; Silica ; Distortion

Citation

Claude A. Klein
"High-energy laser windows: case of fused silica", Opt. Eng. 49(9), 091006 (September 13, 2010). ; http://dx.doi.org/10.1117/1.3484946


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