We present a direct measurement of the displacement noise spectrum of a macroscopic silicon flexure at room temperature. A cantilever attached to the 100 μm thick flexure holds a mirror which forms part of an optical cavity to enhance the displacement sensitivity to thermal noise. We predict the displacement noise spectrum using a simple model that assumes the dominant source of frequency-dependent loss is thermo-elastic damping and find good agreement with the experimental data. The measurement is consistent with a frequency-independent loss of combined with frequency-dependent thermo-elastic damping as the dominant losses. A crossover between the two that occurs well above the flexure resonant frequency allows a broadband measurement of the thermal noise of the silicon flexure. The flexure material, geometry, and measurement band are similar to those of planned future gravitational wave detectors.
Direct observation of the thermal noise spectrum of a silicon flexure membrane
Note: This paper is part of the APL Special Collection on Gravitational Wave Detectors.
D. P. Kapasi, T. T-H. Nguyen, R. L. Ward, J. Eichholz, M. H. Iqbal, T. G. McRae, P. A. Altin, D. E. McClelland, B. J. J. Slagmolen; Direct observation of the thermal noise spectrum of a silicon flexure membrane. Appl. Phys. Lett. 9 January 2023; 122 (2): 022202. https://doi.org/10.1063/5.0131984
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