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Proceedings Paper

Nanosecond 1064nm damage thresholds for bare and anti-reflection coated silica surfaces
Author(s): Arlee V. Smith; Binh T. Do; John Bellum; Rod Schuster; David Collier
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Paper Abstract

We employed the same measurement techniques that have proven successful for bulk damage thresholds measurements to measure damage thresholds of bare silica surfaces polished using various methods and to measure damage thresholds for antireflection coated silica, again for various surface polishes. Light in a single transverse and longitudinal mode, from a Q-switched Nd:YAG laser is focused to an 8 µm spot on the front and rear surfaces of silica windows polished using ceria, alumina, or alumina/silica to find the damage threshold. We repeated the exercise for the same surfaces anti reflection coated with silica/hafnia film stacks. We used surface third harmonic generation to precisely place the focus on the surfaces. Key findings include: 1. The surface damage threshold can be made equal to the bulk damage threshold. There is a large difference in single-pulse damage thresholds of bare silica surfaces polished using ceria, alumina, and alumina followed by silica. The ceria polished samples have a statistical damage threshold ranging from 50 to 450 GW/cm2. The alumina polished surfaces damage at 200-500 GW/cm2, with half the spots damaging at the bulk threshold of 500 GW/cm2. The windows polished by alumina followed by silica damage almost universally at the bulk damage threshold of 500 GW/cm2. 2. There are strong conditioning effects for these surfaces. The ceria polished surfaces have reduced thresholds for multiple pulses. The alumina polished surfaces attain the bulk damage threshold at most locations using multiple pulse annealing. 3. The underlying polishes strongly affect the damage thresholds for the AR coatings. The alumina plus silica polished samples have the highest thresholds, with statistical variations from 150-380 GW/cm2. The alumina polished samples damage at only 50 GW/cm2, but with annealing the threshold rises to 200 GW/cm2, while the ceria polished samples damage at 50-200 GW/cm2 with no strong multiple shot effect. 4. We found there was no beam size variation of the damage threshold irradiance for the bare alumina/silica polished samples. 5. We showed that air breakdown does not limit the surface irradiance, silica breakdown does. 6. We recorded damage morphologies for the different surfaces.

Paper Details

Date Published: 30 December 2008
PDF: 13 pages
Proc. SPIE 7132, Laser-Induced Damage in Optical Materials: 2008, 71321T (30 December 2008); doi: 10.1117/12.804130
Show Author Affiliations
Arlee V. Smith, Sandia National Labs. (United States)
Binh T. Do, Sandia National Labs. (United States)
John Bellum, Sandia National Labs. (United States)
Rod Schuster, Alpine Research Optics (United States)
David Collier, Alpine Research Optics (United States)

Published in SPIE Proceedings Vol. 7132:
Laser-Induced Damage in Optical Materials: 2008
Gregory J. Exarhos; Detlev Ristau; M. J. Soileau; Christopher J. Stolz, Editor(s)

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