Laser Damage Studies of Ion Beam Milled Fused Silica

Abstract

Ion beam figuring is a promising optical fabrication technique in which substrate material is removed from an optical component by selectively ion beam milling the surface. The effects of ion beam milling on the properties of the optical surface are not completely understood. One area of investigation is the influence of ion beam milling on the laser damage threshold of the substrate. The ion milling process removes part of the damage layer at the surface of the optic formed during fabrication, and this might result in modification of laser damage behavior. As part of an investigation of the ion beam figuring process, a study was undertaken to determine the effect of ion milling on the laser damage threshold of fused silica. Fused silica substrates were ion milled to depths up to ten microns using a 1500 eV, 40mA Argon ion beam from a Kaufman ion source. The milled substrates were then subjected to laser damage testing using a 1064 nanometer wavelength laser. The tests were performed using one nanosecond pulse width single shot pulses and sixteen nanosecond pulse width thirty Hz pulses. The results indicate that ion beam milling has no significant influence on the damage threshold.