Nanomechanical resonators based on strained silicon nitride (Si 3 N 4 ) have received a large amount of attention in fields such as sensing and quantum optomechanics due to their exceptionally high quality factors (Qs). Room-temperature Qs approaching 1 billion are now in reach by means of phononic crystals (soft-clamping) and strain engineering. Despite great progress in enhancing Qs, difficulties in fabrication of soft-clamped samples limits their implementation into actual devices. An alternative means of achieving ultra-high Qs was shown using trampoline resonators with engineered clamps, which serves to localize the stress to the center of the resonator, while minimizing stress at the clamping. The effectiveness of this approach has since come into question from recent studies employing string resonators with clamptapering. Here, we investigate this idea using nanomechanical string resonators with engineered clampings similar to those presented for trampolines. Importantly, the effect of orienting the strings diagonally or perpendicularly with respect to the silicon frame is investigated. It is found that increasing the clamp width for diagonal strings slightly increases the Qs of the fundamental out-of-plane mode at small radii, while perpendicular strings only deteriorate with increasing clamp width. Measured Qs agree well with finite element method simulations even for higher-order resonances. The small increase cannot account for previously reported Qs of trampoline resonators. Instead, we propose the effect to be intrinsic and related to surface and radiation losses.
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Document VersionPublisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Christensen, S. L., Johansen, M. M., Michieletto, M., Triches, M., Hout, L., Maack, M. D., & Laegsgaard, J. (2020). Novel high-speed camera analysis of transverse mode instabilities in rod fiber amplifiers. "Novel high-speed camera analysis of transverse mode instabilities in rod fiber amplifiers," Proc. ABSTRACTIn this work a novel accurate method of measuring beam fluctuations is presented and applied to analyze transverse mode instabilities (TMI). The new measurement, ST-measurement, uses Fourier analysis on data from a high-speed camera to achieve raw spatial information about beam fluctuations. TMI in a 65 µm modefield-diameter aeroGain-ROD-PM85 fiber is investigated using both the ST-and standard photo detector measurement. A comparison of the two measurements shows the quantitative and qualitative superiority of the new ST-measurement due to the spatial information. Numerical simulations are carried out to support the interpretation of the data.
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