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The use of low loss materials is of great interest for applications like laser stabilization cavities and opto-mechanical devices. To increase their sensitivity a reduction of the mechanical loss and thermal energy is necessary. In order to achieve a reduction of the thermal noise level these applications operate at cryogenic temperatures. Depending on the material, imperfections, impurities etc., relaxation processes can limit the sensitivity of these devices.

Schwarz et al. (pp. 2719-2723) present a method to characterize the mechanical loss of cylinder shaped, all side polished samples in a temperature range from 5 to 300 K. To minimize additional losses, the sample is suspended in a pendulum configuration (see left figure). The mechanical loss is measured by the excitation of a resonant mode vibration (two figures on the right) and the recording of the free exponential ring-down at a fixed temperature. A sample made from CaF2 showed an unknown peak in the mechanical loss around 25 K (see top figure). Due to the shape of the peak and the frequency dependence it concerns a thermally activated mechanism.