Crystalline Coating Loss Angle Measurement via Mechanical Ringdown on Large-Area Samples

The elastic loss of ~70-mm diameter substrate-transferred crystalline coatings was measured via mechanical ringdown. The loss angles, decomposed into bulk and shear components, (5.33±0.03)×10
^-4
and <; 5.2)×10
^-7
respectively, were incorporated in a finite element model to predict the performance of a 35-mm long cavity with a 250-μm beam waist (radius), yielding a coating loss angle of (4.78±0.05)×10
^-5
, in agreement with published results from direct noise measurements, (4±4)×10
^-5
. This test independently confirms the low-noise performance of GaAs/AlGaAs multilayers and shows that the elastic loss is not degraded with size scaling.