Optical effects of metallic mirror surface modification

The optical effects of radiation damage on metal mirrors of MeV- and keV-ra nge ions have been examined. Al, Cu and Cr ion beams of 1-3 MeV energy were used to bombard Al, Cu and stainless steel mirrors respectively with doses spanning 10-25 dpa. The effects following long-term sputtering with keV-ra nge ions of hydrogen plasma (or deuterium) on mirror reflectivity R in the UV and visible spectral regions were investigated. The modifications of two stainless steel mirrors' optical properties induced by the deposition of d ifferent thicknesses of B layers have also been studied. The ex situ ellips ometric data for multiple angles of incidence (within the interval from 64 to 80 degrees) were recorded at a wavelength of lambda=632.8 nm, before bot h ion irradiation and boronization and after the treatment. It was found th at even short keV-range ion bombardment of Al mirrors drastically changed t heir reflectivity at any given wavelength, in contrast to a stainless steel mirror. The boronization resulted in noticeable changes of the optical con stants in the UV. The optical constants of the boron film on the stainless steel substrate (n=2.53, k approximate to 0), with thicknesses d (d=7.3 and 16.6 nm), were calculated from the ellipsometric data. The IR ellipsometri c measurements within the frequency range 400-5000 cm(-1) were performed fo r stainless steel mirrors pre-irradiated by Cr ions and then coated by B to clarify the damaged layer formation mechanism. The ellipsometric changes h ave been attributed to both modification of the metallic mirrors' surface m irror relief and the formation of a skin layer with better conductivity aft er ion treatment. (C) 1999 Published by Elsevier Science S.A. All rights re served.