Defect insensitive 100 J/cm2multilayer mirror coating process

Abstract

Multilayer mirrors are fluence-limited by nodular defects. Such defects originate from the deposition source, inadequate cleaning, transport, pump down, heating, shedding from rotating hardware, etc. These overcoated inclusions behave as micro-lenses resulting in light intensification within the multilayer structure. To minimize the impact of these defects, a planarization process has been developed to reduce geometric-induced light intensification. By exploiting the angledependent etching rate of materials, a deposit-and-etch process reduces nodular defect height and diameter. Planarized defects demonstrate a greater than 20x increase in laser resistance at a wavelength of 1064 nm and pulse length of 10 ns. Process parameters were explored such as planarization efficiency of the coating materials, discrete versus continuous etching, thick planarization layers for substrate defects, and etching throughout the multilayer to planarize coating defects.