Investigation of the effect of large x-ray fluences on multilayer structures

Abstract

The use of multilayer mirrors in x-ray laser cavities is complicated by extremely intense optical and x-ray pulses that damage the multilayer mirror before it has done its job. The issue of damage of the mirror by x-ray emission from the plasma amplifier has been studied experimentally using short duration (500 psec) bursts of soft x-rays from a laser produced Au plasma. Different damage/failure mechanisms have been observed and identified for Mo/Si, MoSi2/Si, W/C, WC/C and Cr3C2/C multilayers and damage thresholds quantified. The effect of the x-ray flux on the peak mirror reflectivity together with the position and shape of the bandpass has been resolved both temporally and spec­trally. The shape of the bandpass has been fitted to solutions to the Fresnel equations for aperiodic stacks in order to infer the time history of the stack. Rapid diffusion of Mo into Si in Mo/Si multilayers has been observed to occur in time scales of order 70 psec.