Intensity-Dependent Absorption in 10.6-μm Laser-Illuminated Spheres

Abstract

An intensity dependence of the absorption of 10-\ensuremath{\mu} m laser light on C${\mathrm{O}}_{2}$-laser-fusion targets has been observed. Absorption on gold spheres increases from 25%-30% at ${10}^{14}$ W/${\mathrm{cm}}^{2}$ to 50%-60% at ${10}^{16}$ W/${\mathrm{cm}}^{2}$, with most of the variation occurring above ${10}^{15}$ W/${\mathrm{cm}}^{2}$. Concurrently, hot-electron temperature scales as ${T}_{\mathrm{hot}}\ensuremath{\propto}{I}^{0.43}$ over the entire range. The absorption variation is interpreted as enhanced resonant absorption. It is suggested that as intensity is increased, the critical surface in the irradiated region becomes increasingly unstable, thereby permitting greater surface distortion and more favorable coupling conditions for resonant absorption.