Mr. Rod L. Schuster Profile

Rod L. Schuster

Key Account Manager at Newport Corp a division of MKS Instruments

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Publications (3)

Proceedings Article | 29 November 2010 Paper

How to polish fused silica to obtain the surface damage threshold equals to the bulk damage threshold

Troy Alley, Peter Allard, Rod Schuster, David Collier, Arlee Smith, Binh Do, Alice Kilgo

Proceedings Volume 7842, 784226 (2010) https://doi.org/10.1117/12.868416

KEYWORDS: Polishing, Laser damage threshold, Surface finishing, Silica, Pulsed laser operation, Cerium, Oxides, Q switched lasers, Plasma, Laser induced damage

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Proceedings Article | 30 December 2008 Paper

Nanosecond 1064nm damage thresholds for bare and anti-reflection coated silica surfaces

Arlee Smith, Binh Do, John Bellum, Rod Schuster, David Collier

Proceedings Volume 7132, 71321T (2008) https://doi.org/10.1117/12.804130

KEYWORDS: Laser damage threshold, Surface finishing, Polishing, Silica, Antireflective coatings, Reflection, Q switched lasers, Coating, Pulsed laser operation, Cerium

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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.

Proceedings Article | 22 February 2008 Paper

Rate equation model of bulk optical damage of silica, and the influence of polishing on surface optical damage of silica

Arlee Smith, Binh Do, Rod Schuster, David Collier

Proceedings Volume 6873, 68730U (2008) https://doi.org/10.1117/12.774620

KEYWORDS: Laser damage threshold, Silica, Surface finishing, Polishing, Picosecond phenomena, Optical damage, Pulsed laser operation, Plasma, Q switched lasers, Ionization

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Our objective is to understand the mechanism that generates catastrophic optical damage in pulsed fiber amplifiers. We measured optical damage thresholds of bulk fused silica at 1064 nm for 8 ns and 14 ps pulses. The 8 ns pulse is single longitudinal mode from a Q-switched laser, and the 14 ps pulse is from a Q-switched mode-lock laser. The beams in both cases are TEM₀₀ mode, and they are focused to a 7.5 μm spot inside a fused silica window. The pulse-to-pulse energy variations are 1% for 8 ns pulses and 5% for 14 ps pulses. Under these conditions optical damage is always accompanied by plasma formation at the focal spot; we found the damage threshold fluences are 3854 ± 85 J/cm² for the 8 ns pulses and 25.4 ± 1.0 J/cm² for the 14 ps pulses. These fluences are corrected for self focusing. Both damage thresholds are deterministic, in contrast to the claim often made in the literature that optical damage is statistical in the nanosecond range. The measured damage threshold fluences for 8 ns and 14 ps pulses do not fit a square root of pulse duration scaling rule. We interpret the damage in terms of plasma formation initiated by multiphoton ionization and amplified by an electron avalanche. The damage threshold irradiance can be matched with a simple rate equation model that includes multiphoton ionization, electron avalanche, and electron-hole recombination. The damage morphologies are dramatically different in the nanosecond and picosecond cases because of the large difference in deposited energy. However, both morphologies are reproducible from pulse to pulse. We also measured surface damage thresholds for silica windows polished by different methods. We find that cerium oxide polished surfaces damage at approximately 40% of the bulk threshold, with a large statistical spread. Surfaces prepared using an Al₂O₃ polish damaged between 50% and 100% of the bulk damage limit, with a substantial fraction at 100%. Surfaces polished using first the Al₂O₃ polish and then an SiO₂ polish exhibit surface damage values equal to the bulk damage value at nearly every point. We also measured damage thresholds for different sized focal spots. Some earlier reports have claimed that damage thresholds depend strongly on the size of the focal spot, but we find the surface threshold is independent of the spot size.

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