激光窗口热效应和应力双折射的分析

Analysis on thermal effect and stress-birefringence of laser window

分析了平板窗口在激光加热和内外压强差作用下对光束带来的附加相移,详细讨论了应力双折射部分的相移,计算了CaF2窗口的温升、应力、附加相移、远场Strehl比和退偏度等的分布。结果表明:窗口变形和折射率随温度变化是产生附加相移的主要原因,窗口的非均匀温升将导致光束质量下降,应力双折射部分的相移与窗口表面Miller指数有关,对入射光产生一定的退偏效应,从而影响光束质量。

The phaseshifts induced by thermal effect and pressure difference between outer-surface and inner-surface of plane laser window are analysed. The phaseshifts caused by stress-birefringence are discussed. Distributions of temperature increment, stress, phaseshifts, Strehl-ratio and depolarization are calculated. It is indicated that window deformation and refractive index changing with temperature are primary factors of phaseshifts and result from non-uniformity of temperature increment, making beam quality declining. Stress-birefringence is related with Miller indices of laser window surface, which results in depolarization and also affects beam quality.