15 January 2007 Direct measurements of residual absorption in fluoridic thin films and optical materials for DUV laser applications
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Abstract
The absorption of ArF laser pulses in calcium fluoride, fused silica as well as in highly (HR) and partially (PR) reflecting fluoridic coatings is directly measured using the laser induced deflection technique (LID). For the calcium fluoride sample it is proved that the LID technique allows to separate surface and bulk absorption by measuring only one sample with the size 20 x 20 x 10 mm3. At a laser pulse fluence Φ = 36 mJ/cm2 and a repetition rate f = 1 kHz the bulk absorption coefficient and the surface absorption are determined to 0.0029 cm-1 and 0.00043 (two surfaces), respectively. For the HR and PR coatings the ArF laser absorption is 0.0004 for Φ= 22 mJ/cm2 (f = 1 kHz) and 0.0066 for Φ= 40 mJ/cm2 (f = 1 kHz), respectively. For the example of the PR coating the influence of high coating scattering on the LID measurements is discussed and an appropriate measuring procedure is derived and applied to avoid the scattering influence. In addition to the established LID setup requiring rectangular substrate dimensions a modified setup is introduced enabling the measurement of cylindrical optical elements. The principle of the new LID setup is explained and first measurements at fused silica are presented.
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Ch. Mühlig, Ch. Mühlig, W. Triebel, W. Triebel, S. Kufert, S. Kufert, Ch. Noppeney, Ch. Noppeney, H. Bernitzki, H. Bernitzki, } "Direct measurements of residual absorption in fluoridic thin films and optical materials for DUV laser applications", Proc. SPIE 6403, Laser-Induced Damage in Optical Materials: 2006, 640317 (15 January 2007); doi: 10.1117/12.695438; https://doi.org/10.1117/12.695438
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