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Proceedings Paper

1.064-um laser damage studies of silicon oxy-nitride narrow band reflectors
Author(s): Jonathan R. Milward; Keith L. Lewis; K. Sheach; Rudolf August Heinecke
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Paper Abstract

In a paper presented at the 1992 Boulder Damage Symposium, we discussed the role of electric field effects, defect type, surface roughness, film thickness and coating absorption on the laser damage thresholds of sinusoidally modulated, plasma deposited, silicon oxy-nitride narrow band reflectors. We concluded that the damage threshold, which was essentially constant at 2 J/cm2 at the test wavelength of 0.532 micrometers , was defect dominated. A sizeable fraction of the damage events occurred at a particular type of defect--a hemispherical hillock feature typically 5 micrometers in diameter as identified by SEM and interferometric surface profiling. We postulated that this defect initiated damage because of either a microlensing effect or an enhanced electric field effect. We have since measured the laser damage thresholds of all these samples at 1.064 micrometers , and found significant variations in the damage thresholds, which were a factor of three higher on average than those at 0.532 micrometers . The microlens model presented can explain damage thresholds up to a factor of four higher at the longer wavelength, and predicts a minimum nodule height for increased damage susceptibility. The minimum nodule height is dependent on the wavelength and the coating average index. The wavelength scaling of the fluence enhancement and the minimum nodule height imply that nodule initiated damage will become an even more serious problem as the wavelength approaches the UV.

Paper Details

Date Published: 28 July 1994
PDF: 8 pages
Proc. SPIE 2114, Laser-Induced Damage in Optical Materials: 1993, (28 July 1994); doi: 10.1117/12.180925
Show Author Affiliations
Jonathan R. Milward, Defence Research Agency (United Kingdom)
Keith L. Lewis, Defence Research Agency (United Kingdom)
K. Sheach, BNR Europe Ltd. (United Kingdom)
Rudolf August Heinecke, BNR Europe Ltd. (United Kingdom)

Published in SPIE Proceedings Vol. 2114:
Laser-Induced Damage in Optical Materials: 1993
Harold E. Bennett; Lloyd L. Chase; Arthur H. Guenther; Brian Emerson Newnam; M. J. Soileau, Editor(s)

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