PHOTOELASTIC MEASUREMENT OF ANELASTICITY AND ITS IMPLICATIONS FOR GRAVITATIONAL-WAVE INTERFEROMETERS

We have developed a method to determine the internal friction over a w ide range of frequencies in transparent materials such as fused silica . We measure the anelastic aftereffect, the relaxation of a sample aft er a steady stress is removed, by sensing the polarization of a beam o f light that traverses the sample. The fractional relaxation of the sa mple on a given time scale is a direct measure of the anelastic loss a ngle of the material at the corresponding frequency. To date, we have achieved sensitivity to loss angles as small as 10(-6). We discuss the relevance of these measurements for the design of interferometric det ectors of gravitational waves. (C) 1998 American Institute of Physics. [S0034-6748(98)02306-5]