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Optical Engineering

Absorption measurement of high-reflectance coated mirrors at 193 nm with a Shack-Hartmann wavefront sensor
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Paper Abstract

All dielectric high-reflectance (HR) mirror coatings consisting of AlF3/LaF3/oxide layers were deposited on deep-ultraviolet-grade fused silica and CaF2. A novel technique was employed to measure the absorption of these mirrors during irradiation by a 193-nm ArF excimer laser source. The method involves the application of a photothermal measurement technique. The setup uses a Shack-Hartmann wavefront sensor to measure wavefront deformation caused by the heating of the coating by the ArF beam. Laser calorimetric measurements of absorption were used to calibrate the wavefront sensor. The new test setup was used to investigate HR mirror coatings both before and after exposure to high average power ArF laser beams. HR mirror samples were irradiated by a 193-nm kilohertz laser source for either 500 million or 18.6 billion pulses. The differences between wavefront distortion measured inside the beam footprint compared to measured outside the beam footprint can be explained by compaction of the coating in the area heated by the ArF laser. Interesting wavefront-distortion results from testing mirrors with either fused silica or CaF2 substrates can be explained by considering the figure of merit of these materials for excimer-laser mirror substrates.

Paper Details

Date Published: 10 July 2012
PDF: 6 pages
Opt. Eng. 51(12) 121803 doi: 10.1117/1.OE.51.12.121803
Published in: Optical Engineering Volume 51, Issue 12
Show Author Affiliations
Byungil Cho, Newport Corp. (United States)
Edward J. Danielewicz, Newport Corp. (United States)
J. Earl Rudisill, Newport Corp. (United States)


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