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12 April 2001 Optical measurement of UV absorption in dielectric coatings
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Nonlinear absorption phenomena are of great interest for the investigation of laser induced damage processes in dielectric materials. Up to now, photothermal techniques like thermal lensing and laser calorimetry are the only methods, which have been successfully applied for measurements on nonlinear absorption in optical coatings in the UV spectral range. Here, the knowledge of thermophysical properties of the investigated samples is required for both laser calorimetry and thermal lensing, for the determination of absolute absorption values. To overcome this restriction a pure optical determination of absorption effects in dielectrics during excimer laser irradiation is presented for Al2O3 and SiO2 single layers as well as for a Al2O3/SiO2 high reflecting multilayer deposited on quartz. During the laser pulse, both transmittance and reflectivity were measured simultaneously and indicated a significant dependence to the intensity of the laser beam. Excluding a possibly existing influence of thermal detuning by estimation of its order of magnitude, the transient optical absorption inside the film was shown to be dominant in accordance with the results obtained by thermal lens technique. In case of the Al2O3/SiO2 high reflecting coating the UV radiation resistivity at (lambda) equals 193 nm should only be determined by nonlinear absorption.
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S. Martin, S. Bock, Eberhard Welsch, and Holger Blaschke "Optical measurement of UV absorption in dielectric coatings", Proc. SPIE 4347, Laser-Induced Damage in Optical Materials: 2000, (12 April 2001);

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