SEDL / STP / STP759-EB / STP37006S

A New Photographic Technique for Observing Bulk Laser Damage

Thomas, N
Lawrence Livermore National Laboratory, University of California, Livermore, California

Sonderman, J
Lawrence Livermore National Laboratory, University of California, Livermore, California

Stokowski, S
Lawrence Livermore National Laboratory, University of California, Livermore, California

Wallerstein, P
Lawrence Livermore National Laboratory, University of California, Livermore, California

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

Pages: 11    Published: Oct 1981

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Abstract

A damage site camera was developed to record the onset of bulk laser damage in materials. The camera images and magnifies the damage track using forward-scattered laser light. Employing this camera we can detect the presence of very small (<10 μm) damage sites with densities as low as 10/cc. The camera is used at oblique incidence.

We have observed discrete damage sites generated within the bulk of some materials, such as silicate glass, fluorophosphate glass, and KDP crystals, by 1-ns, 1064-nm laser pulses. The energy fluxes at which bulk damage is initiated are in the range of 2 to 20 J/cm², much lower than the fluxes required to cause damage by intrinsic processes. Small foreign inclusions (<1 μm diameter) are the cause of these low bulk damage thresholds. The inclusion density varies from 10⁷/cc to less than 10/cc. At threshold the damaged volumes are small (1–5 μm in diameter) and thus, can be observed most easily by their forward-scattered light.

Several photographs are shown to illustrate the onset of bulk laser damage in fluorophosphate glass and KDP crystals.