SEDL / STP / STP1028-EB / STP18589S

Impact of Thermal Blooming on Laser Damage Measurement Accuracy

Newnam, BE
Los Alamos National Laboratory, Los Alamos, New Mexico

Pages: 1    Published: Jan 1988

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Abstract

The presence of thermal blooming in laser damage experiments conducted in air frequently goes unnoticed. For certain conditions, however, this effect can result in significant errors in determining the magnitude of damage thresholds.

Thermal blooming of a laser beam is a direct result of nonuniform heating of the transmitting medium (air) across the laser beam diameter. The resultant changes in refractive index cause the laser beam to diverge. In a laser damage experiment the test sample is often placed in the focal plane of a positive lens. With thermal blooming, however, the actual focus of the high-intensity laser beam can occur significantly in front of the sample, resulting in overestimates of the damage threshold.

Using the formulation of Skinner for a focused Gaussian beam, we calculate the magnitude of possible errors for damage thresholds of surfaces and thin films measured in air with various wavelengths. Measurements reported by several laboratories fall in the parameter space for which corrections for the effects of thermal blooming are recommended.