Removal of laser-induced damage sites provides a possible mitigation pathway to improve damage resistance of coated multilayer dielectric mirrors. In an effort to determine the optimal mitigation geometry which will not generate secondary damage precursors, the electric field distribution within the coating layers for a variety of mitigation shapes under different irradiation angles has been estimated using the finite difference time domain (FDTD) method. The coating consists of twenty-four alternating layers of hafnia and silica with a quarter-wave reflector design. A conical geometrical shape with different cone angles is investigated in the present study. Beam incident angles range from 0° to 60° at 5° increments. We find that light intensification (square of electric field, |E|²) within the multilayers depends strongly on the beam incident direction and the cone angle. By comparing the field intensification for each cone angle under all angles of incidence, we find that a 30° conical pit generates the least field intensification within the multilayer film. Our results suggest that conical pits with shallow cone angles (≤ 30°) can be used as potential optimal mitigation structures.

Date Published: 31 December 2009
PDF: 9 pages
Proc. SPIE 7504, Laser-Induced Damage in Optical Materials: 2009, 75040M (31 December 2009);

Published in SPIE Proceedings Vol. 7504:
Laser-Induced Damage in Optical Materials: 2009
Gregory J. Exarhos; Vitaly E. Gruzdev; Detlev Ristau; M. J. Soileau; Christopher J. Stolz, Editor(s)