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Developing a more useful surface quality metric for laser optics (Photonics West, Jan., 2011)

This paper reviews the limitations of traditional surface quality inspection techniques, and explores the use of a quantitative inspection method based on a microscope, calibrated lighting, a CCD detector and image processing software.

Light scatter due to surface defects on laser resonator optics produces losses which lower system efficiency and output power. The traditional methodology for surface quality inspection involves visual comparison of a component to scratch and dig (SAD) standards under controlled lighting and viewing conditions. Unfortunately, this process is subjective and operator dependent. Also, there is no clear correlation between inspection results and the actual performance impact of the optic in a laser resonator. As a result, laser manufacturers often overspecify surface quality in order to ensure that optics will not degrade laser performance due to scatter. This can drive up component costs and lengthen lead times. Alternatively, an objective test system for measuring optical scatter from defects can be constructed with a microscope, calibrated lighting, a CCD detector and image processing software. This approach is quantitative, highly repeatable and totally operator independent. Furthermore, it is flexible, allowing the user to set threshold levels as to what will or will not constitute a defect. This paper details how this automated, quantitative type of surface quality measurement can be constructed, and shows how its results correlate against conventional loss measurement techniques such as cavity ringdown times.

This paper was originally published by the SPIE at Photonics West 2011:

Trey Turner and Quentin Turchette, “Developing a more useful surface quality metric for laser optics,” Solid State Lasers XX: Technology and Devices, W. Andrew Clarkson; Norman Hodgson; Ramesh Shori, Editors, Proc. SPIE 7912, 791213 (2011)

Copyright 2011 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.


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