Studying Laser Induced Damage from Defects

Studying Laser Induced Damage from Defects

A statistical study of the relationship between surface quality and laser induced damage (SPIE)

This study attempts to establish a correlation between observed coating defects and laser damage (from a 1064 nm laser in the nanosecond regime), utilizing a large 
sample size from a single coating run, together with the actual fluence levels present at the defect sites.

This paper explores why traditional laser damage testing routinely fails to accurately characterize and predict component damage threshold. Its goal is to advance the state of knowledge regarding laser damage in a direction that might ultimately lead to a test that is truly predictive of the actual probability of damage at any fluence.

Laser induced damage of optical components is a concern in many applications in the commercial, scientific and military market sectors.  Numerous component manufacturers supply “high laser damage threshold” (HLDT) optics to meet the needs of this market, and consumers pay a premium price for these products.  While there’s no question that HLDT optics are manufactured to more rigorous standards (and are therefore inherently more expensive) than conventional products, it is not clear how this added expense translates directly into better performance.  This is because the standard methods for evaluating laser damage, and the underlying assumptions about the validity of traditional laser damage testing, are flawed.  In particular, the surface and coating defects that generally lead to laser damage (in many laser-parameter regimes of interest) are widely distributed over the component surface with large spaces in between them.  As a result, laser damage testing typically doesn’t include enough of these defects to achieve the sample sizes necessary to make its results statistically meaningful.  The result is a poor correlation between defect characteristics and damage events.  This paper establishes specifically why this is the case, and provides some indication of what might be done to remedy the problem. 

This paper was originally published by the SPIE at Laser Damage 2012:

Trey Turner, Quentin Turchette and Alex R. Martin, “A statistical correlation study between surface quality and LIDT at 1064 nm,” Thin Films II, Mireille Commandré and Vitaly E. Gruzdev, Editors, Proc. SPIE 8530, (2012)

Copyright 2011 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.

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