SYMPOSIA PAPER Published: 01 January 1985

Toward Improved Accuracy in Limited-Scale Pulsed Laser Damage Testing Via the “Onset Method”


A recently reported method for determining the defect damage onset (minimum intensity for defect initiated damage) in optical surfaces offers certain advantages over more conventional methods. First of all, the onset is a more reliable and useful indication of operational performance than conventionally measured thresholds, which may depend strongly on the size of the tested area. Secondly, measurement of damage frequency vs intensity provides valuable information on defect densities. This permits more effective use of a limited test area and provides a basis for defect classification. Effective limited-scale testing is becoming increasingly important as larger optical surfaces and reduced defect densities are made possible by improved coating technology.

In this paper, the onset method is mainly applied to 1.06 μm coatings, tested with a 40 μm (D-1/e2) Gaussian focal spot and 2.7 μm coatings, tested with a 67 μm spot. Comparisons are made between onsets and conventionally measured thresholds, including a demonstration of convergence with large-spot thresholds from other laboratories. Examples of damage frequency distributions indicating the presence of more than one class of defect will also be shown. Finally, the onset model is extended to include flat-topped spatial profiles, and possible advantages over Gaussian profiles are noted.

Author Information

Seitel, SC
Porteus, JO
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Developed by Committee: F01
Pages: 502–512
DOI: 10.1520/STP29005S
ISBN-EB: 978-0-8031-4956-4
ISBN-13: 978-0-8031-0930-8