13 May 1997 High reflector absorptance measurements by the surface thermal lensing technique
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Abstract
Surface thermal lensing is an alternate configuration of a photothermal deflection system that was used to measure low levels of optical absorption. The thermal lensing configuration facilitated the alignment of the pump and prove laser beams by using a larger diameter probe beam. This technique was applied to high performance optical coatings, specifically high reflectors at 511 nm, zero degrees angle of incidence. The absorptance of these coatings was previously measured using a high power copper vapor laser system. A high power copper laser beam is focused onto an approximately 2 mm diameter spot. A thermal camera senses the temperature rise with respect to the rest of the coating. The temperature change, power density and beam diameter were used with an empirical formula that yields optical absorption. The surface thermal lensing technique was able to resolve absorption levels lower than that achieved with the copper laser method.
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Robert Chow, John R. Taylor, Zhouling Wu, Rene Krupka, Tian Li Yang, "High reflector absorptance measurements by the surface thermal lensing technique", Proc. SPIE 2966, Laser-Induced Damage in Optical Materials: 1996, (13 May 1997); doi: 10.1117/12.274226; https://doi.org/10.1117/12.274226
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KEYWORDS
Laser beam diagnostics

Optical coatings

Reflectors

Absorption

Copper vapor lasers

Signal detection

High power lasers

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