SEDL / STP / STP1015-EB / STP18717S

A Versatile Laser Glass Inspection and Damage Testing Facility

Marion, JE
Lawrence Livermore National Laboratory University of California, Livermore, California

Greiner, GJ
Lawrence Livermore National Laboratory University of California, Livermore, California

Campbell, JH
Lawrence Livermore National Laboratory University of California, Livermore, California

Chaffee, PH
Lawrence Livermore National Laboratory University of California, Livermore, California

Hildum, JS
Lawrence Livermore National Laboratory University of California, Livermore, California

Grens, JZ
Lawrence Livermore National Laboratory University of California, Livermore, California

Weinzapfel, CL
Lawrence Livermore National Laboratory University of California, Livermore, California

Winfree, SM
Lawrence Livermore National Laboratory University of California, Livermore, California

Milam, D
Lawrence Livermore National Laboratory University of California, Livermore, California

Pages: 4    Published: Jan 1988

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Abstract

Most glass optical components for high power lasers are melted and homogenized in platinum-lined crucibles leading to the potential presence of microscopic platinum inclusions. In situations where large optics are exposed to high laser fluences, a significant problem can be created by an extremely low density of inclusions, as low as one per component. Previously, direct visual examination or optical microscopy was used to inspect for these particles, limiting reliable detection to inclusions greater than 10μm diameter. Unfortunately, much smaller inclusions can initiate damage in modern lasers operated at high fluences.

A test facility is described which detects small opaque inclusions in large transparent components by using a commercial laser which delivers high energy pulses to the test sample at moderate frequency in a small diameter beam. The sample is automatically scanned such that each point in the volume is irradiated with ten pulses at twice the inclusion damage threshold--an amount sufficient to cause visible damage at inclusion sites. This approach permits detection of opaque inclusions in the parts per trillion and lower concentration range. The specifics of the device design, and its performance are discussed in the context of automatic inclusion inspection and mapping in large laser optics.