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Proceedings Paper

Picosecond-nanosecond bulk damage of fused silica at 1064nm
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Paper Abstract

We are interested in maximizing the performance of fiber lasers and amplifiers, particularly for amplification of ps-ns pulses. The observed pulse energies from large mode area fiber amplifiers routinely exceed the reported bulk damage threshold of silica. We have undertaken a program to establish the intrinsic damage thresholds of silica that are relevant for fiber applications. We use a single transverse / single longitudinal mode Q-switched Nd:YAG laser focused to an 8-µm spot several Rayleigh ranges deep in silica windows for the nanosecond measurement, and a Q-switched, mode locked Nd:YAG laser for the picoseconds measurements. Our key findings include: 1. The damage threshold is deterministic rather than statistical for both ns and ps pulses. The threshold varies less than 1% from location to location. 2. The intrinsic damage threshold of silica is 475±25 GW/cm2 (fluence = 3850 J/cm2) for 8 ns pulses and approximately 3 times higher for 14 ps pulses. 3. There is no difference in damage thresholds among Corning's A0, B1, C1, D1, D2, and D5 grades of silica. 4. A tight focus is required to avoid large self focusing corrections and to avoid SBS for the 8-ns pulses. 5. Damage morphologies are reproducible from pulse to pulse but change with focal spot size and pulse duration. In all cases, damage appears to begin exactly at the focus and then move upstream approximately one Rayleigh range. 6. The dependence of the damage threshold fluence on pulse duration is nearly linear for pulse durations longer than 50 ps. The square root of duration dependence reported by several investigators for the 50 ps to 10 ns range is refuted. 7. The variation of damage fluence with pulse duration from 20 fs to 20 ns and beyond is well described by a single electron avalanche rate equation with three fixed rates for the avalanche, multiphoton ionization, and electron recombination terms. 8. Our damage threshold is consistent with the most reliable DC field breakdown threshold. 9. We verified in detail the self focusing corrections and the SBS thresholds for our measurement conditions. 10. The damage threshold is affected little by mechanical strain at levels similar to those in polarization-preserving fiber.

Paper Details

Date Published: 30 December 2008
PDF: 16 pages
Proc. SPIE 7132, Laser-Induced Damage in Optical Materials: 2008, 71321E (30 December 2008); doi: 10.1117/12.804129
Show Author Affiliations
Arlee V. Smith, Sandia National Labs. (United States)
Binh T. Do, Sandia National Labs. (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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