Damage to Large Optics by Focusing Acoustic Transients: Revision 2.

摘要

We have observed damage to 80-cm-diam fused-silica disks and lenses subjected to high-fluence pulses (up to 2.3 J/cm(sup 2)) from an upgraded Nova laser beamline (wavelength 351 nm; pulse duration 2.35 ns; beam diameter 70 cm; energy up to 8 kJ). Damage occurred in the center of each element, where a 6-cm-wide obscuration prevented direct illumination. We believe that light strongly scattered by transverse stimulated Brillouin scattering (SBS) interacts with the surface and with the bulk of the substrate, producing two kinds of acoustic waves that propagate to its center, where they become strong enough to do damage. We propose design rules for avoiding acoustic damage in large optics and compare observed thresholds for transverse SBS with predictions in the literature. 7 refs., 8 figs., 1 tab.