Thermal noise arising from mechanical dissipation in oxide coatings is a major limitation to many precision measurement systems, including optical frequency standards, high-resolution optical spectroscopy and interferometric gravity wave detectors. Presented here are measurements of dissipation as a function of temperature between 7 K and 290 K in ion-beam-sputtered Ta 2 O 5 doped with TiO 2 , showing a loss peak at 20 K. Analysis of the peak provides the first evidence of the source of dissipation in doped Ta 2 O 5 coatings, leading to possibilities for the reduction of thermal noise effects.
Here we report the first results comparing the temperature dependence of the mechanical dissipation in thin films of Ta 2 O 5 and Ta 2 O 5 doped with TiO 2 , of a type suitable for use in the multilayer optical coatings for advanced gravitational wave detectors. The results indicate that doping Ta 2 O 5 with TiO 2 can significantly alter the distribution of activation energies associated with the low temperature dissipation peak.
Abstract. Mechanical Q-factor measurements of single crystalline calcium fluoride CaF 2 bulk material are presented. Resonant modes between 27 and 100 kHz were investigated on a cylindrical test sample (∅ 75 mm × 75 mm). For selected modes low temperature measurements of the mechanical Q-factor were done within a temperature range from 5 to 300 K. For the Q-measurements a ring-down technique was used. The substrate was suspended as a pendulum by means of a tungsten wire loop. The highest Q-factor has been achieved around 60 K with 3 × 10 8 which is the highest Q-factor reported on CaF 2 up to now.
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