Continuous-wave laser particle conditioning: Thresholds and time scales

Brown, Andrew; Ogloza, Albert; Olson, Kyle; Talghader, Joseph J.

doi:10.1016/j.optlastec.2016.09.030

Cited by 4 publications

(3 citation statements)

References 10 publications

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“…The 7 µm carbon particles used in laser damage testing are relatively close in size and shape to the 1 µm graphite flakes for which the TCC estimate was calculated and for the model a TCC of 48 kWm −2 K −1 was found to best fit the experimental data. This value is so close to the value measured by direct TCC measurements 14 that it is considered to be a strong indicator of the validity of the model.…”

Section: Resultssupporting

confidence: 79%

“…In the model an average value of 20 000 ppm was used. TCC values were previous calculated at 46 kWm −2 K −1 during laser conditioning experiments of 1 µm graphite flakes 14 . To gain an understanding of the meaning of this value, typical metal-metal mechanical contacts generally have a TCC on the order of a few kWm −2 K −1 15 .…”

Section: Resultsmentioning

confidence: 99%

“…For simplicity the cross sectional area of the particle is assumed to remain constant as the particle evaporates though in practice images of the residue left behind from removed particles are often slightly larger 14 . The simplification used to obtain equation 5 is not valid for the lower irradiances at which many of the DBR coatings failed.…”

Section: Resultsmentioning

confidence: 99%

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Physical Origin of Early Failure for Contaminated Optics

Brown

Bernot

Ogloza

et al. 2019

Sci Rep

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Laser-Induced optical breakdown often occurs unexpectedly at optical intensities far lower than those predicted by ultra-short pulse laser experiments, and is usually attributed to contamination. To determine the physical mechanism, optical coatings were contaminated with carbon and steel microparticles and stressed using a 17 kW continuous-wave laser. Breakdown occurred at intensity levels many orders of magnitude lower than expected in clean, pristine materials. Damage thresholds were found to strongly follow the bandgap energy of the film. A thermal model incorporating the particle absorption, interface heat transfer, and free carrier absorption was developed, and it explains the observed data, indicating that surface contamination heated by the laser thermally generates free carriers in the films. The observed bandgap dependence is in direct contrast to the behavior observed for clean samples under continuous wave and long-pulse illumination, and, unexpectedly, has similarities to ultra-short pulse breakdown for clean samples, albeit with a substantially different physical mechanism.

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Section: Resultssupporting

confidence: 79%

Section: Resultsmentioning

confidence: 99%