Abstract
The standardization and comparison of laser-damage protocols and results are essential prerequisites for development and quality control of large optical components used in high-power laser facilities. To this end, the laser-induced–damage thresholds of two different coatings were measured in a round-robin experiment involving five well-equipped damage testing facilities. Investigations were conducted at the wavelength of 1 μm in the sub picosecond pulse duration range with different configurations in terms of polarization, angle of incidence, and environment (air versus vacuum). In this temporal regime, the damage threshold is known to be deterministic, i.e., the continuous probability distribution transitions from 0 to 1 over a very narrow fluence range. This in turn implies that the damage threshold can be measured very precisely. These characteristics enable direct comparison of damage-threshold measurements between different facilities, with the difference in the measured values indicating systematic errors or other parameters that were not previously appreciated. The results of this work illustrate the challenges associated with accurately determining the damage threshold in the short-pulse regime. Specifically, the results of this round-robin damage-testing effort exhibited significant differences between facilities. The factors to be taken into account when comparing the results obtained with different test facilities are discussed: temporal and spatial profiles, environment, damage detection, sample homogeneity, and nonlinear beam propagation.
Highlights
They are expressed in energy density, and reported based on the beam normal, that is to say that the beam area on the layers is not corrected for the angle of incidence
A material is characterized by its intrinsic laser-induced damage threshold (LIDTint), a property of the material independent of experimental conditions such as the angle of incidence and the state of polarization of the beam. These last two parameters act on the maximum value of the electric field intensity (EFI) and on its position within the material
Intrinsic LIDT values are quite similar, with differences of less than 3%. These results suggest that ‘intrinsically’, environment should have a negligible effect on the damage thresholds of these samples
Summary
The increase in energy and/or power of short-pulse–class lasers (OMEGA-EP [1], PETAL [2], ARC [3]) in the picosecond regime requires components always more resistant to laser intensities, whether these are the compression gratings [4] or the mirrors that transport the beams to the target [5, 6]. Before even dealing with the representativeness of the measurement, it is just as relevant to question the reproducibility of tests carried out on different set-ups Reproducibility in this instance is based on comparing measurements performed according to nominally the same protocol but on different facilities. The objective of the work reported consisted of comparing results of Laser-InducedDamage-Threshold (LIDT) on two dielectric materials (HfO2 and SiO2) in the form of monolayers tested on five different laser facilities. The latter have very similar characteristics such as similar wavelengths (around 1 m), pulse duration (0.8 ps), and beam size. After the presentation of the raw results of LIDT measurements obtained using the various installations, the second part of the article endeavors to identify and analyze the various parameters which are hypothesized to be the sources for the observed discrepancies between these measurements
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