Surface Studies with Acoustic Probe Techniques

Abstract

A new measurement technique is discussed which utilizes acoustic surface waves to detect the surface depth dependence of radiative absorption. We present a theoretical analysis of the detection process which relates these measurements to a quantitative model of surface absorption phenomena. This technique is generally applicable to study weak surface absorption at wavelengths for which a material is essentially transparent. Surface wave phase variations induced by the absorption of 10.6μm radiation have been measured on KC1 surfaces. The surface absorption o of these samples was also measured by calorimetry to be σ~2×10⁻⁴. A radiative pulse of 100 msec and 5 joules incident energy has been observed to induce an 80 mrad phase change. Shorter radiative pulses (~10 msec) are necessary to probe the temperature depth gradient arising from a depth variation of the absorption coefficient. Initial results of recent studies to measure the depth dependence of surface radiative absorption on etched alkali halide surfaces are presented.

Research supported by Advanced Research Projects Agency