1.064-um laser damage studies of silicon oxy-nitride narrow band reflectors

Jonathan R. Milward; Keith L. Lewis; K. Sheach; Rudolf August Heinecke

doi:10.1117/12.180925

28 July 1994 1.064-μm laser damage studies of silicon oxy-nitride narrow band reflectors

Jonathan R. Milward, Keith L. Lewis, K. Sheach, Rudolf August Heinecke

Author Affiliations +

Proceedings Volume 2114, Laser-Induced Damage in Optical Materials: 1993; (1994) https://doi.org/10.1117/12.180925
Event: Laser-Induced Damage in Optical Materials: 1993, 1993, Boulder, CO, United States

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.

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Jonathan R. Milward, Keith L. Lewis, K. Sheach, and Rudolf August Heinecke "1.064-μm laser damage studies of silicon oxy-nitride narrow band reflectors", Proc. SPIE 2114, Laser-Induced Damage in Optical Materials: 1993, (28 July 1994); https://doi.org/10.1117/12.180925

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