Deterministic nanosecond laser-induced breakdown thresholds in pure and Yb3+ doped fused silica

Arlee Smith; Binh Do; Mikko Soderlund

doi:10.1117/12.701399

23 February 2007 Deterministic nanosecond laser-induced breakdown thresholds in pure and Yb³⁺ doped fused silica

Arlee Smith, Binh Do, Mikko Soderlund

Proceedings Volume 6453, Fiber Lasers IV: Technology, Systems, and Applications; 645317 (2007) https://doi.org/10.1117/12.701399
Event: Lasers and Applications in Science and Engineering, 2007, San Jose, California, United States

Abstract

The objective of this work is to understand catastrophic optical damage in nanosecond pulsed fiber amplifiers. We used a pulsed, single longitudinal mode, TEM₀₀ laser at 1.064 µm, with 7.5-nsec pulse duration, focused to a 7.45-&mgr;m-radius spot in bulk fused silica. Our bulk damage threshold irradiance is corrected to account for self focusing. The pulse to pulse variation in the damage irradiance in pure silica is less than 1%. Damage is nearly instantaneous, with an induction time much less than 1 ns. These observations are consistent with an electron avalanche rate equation model, using reasonable rate coefficients. The bulk optical breakdown threshold irradiance of pure fused silica is 5.0x1011 ±7% Watts/cm². We also measured the surface damage threshold irradiance of 1% Yb³⁺ doped fused silica preform of Liekki Yb1200 fiber, and found it is equal to that of pure silica within 2%. The optical damage morphology is reproducible from pulse to pulse. To facilitate the morphology study we developed a technique for locating the laser focus based on the third harmonic signal generated at the air-fused silica interface. This gives a very small uncertainty in focal position (~ 10 &mgr;m) which is important in interpreting the damage structure. The surface third harmonic method was also used to determine the laser focus spot size and verify beam quality. Earlier reports have claimed that the damage irradiance depends strongly on the size of the focal spot. We varied the focal volume to look for evidence of this effect, but found none.

Citation Download Citation

Arlee Smith, Binh Do, and Mikko Soderlund "Deterministic nanosecond laser-induced breakdown thresholds in pure and Yb³⁺ doped fused silica", Proc. SPIE 6453, Fiber Lasers IV: Technology, Systems, and Applications, 645317 (23 February 2007); https://doi.org/10.1117/12.701399

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