Studies of radiative absorption at KCl surfaces using acoustic techniques

Abstract

The application of an acoustic technique to measure surface radiative absorption in highly transparent materials is presented. Dispersive phase changes in acoustic surface wave propagation are induced by the absorption of 10.6-μm pulsed laser radiation on KCl surfaces. Analysis based upon an absorbing surface layer model provides a ±15% determination of both the total surface absorption σ=4.5×10−4 and a bulk absorption coefficient βB=2×10−3 cm−1 for a mechanically polished/chemically etched surface. After mechanical repolishing, this sample yields σ=11.3×10−4. The sensitivity of this technique indicates the possibility of measuring a surface absorption as small as σ≲10−5 and also obtaining details of the radiative absorption depth distribution.