  Milligram-scale resonators have been shown to be suitable for the creation of
3-mode optoacoustic parametric amplifiers, based on a phenomena first predicted
for advanced gravitational-wave detectors. To achieve practical optoacoustic
parametric amplification, high quality factor resonators are required. We
present millimetre-scale silicon resonators designed to exhibit a torsional
vibration mode with a frequency in the 10^5 - 10^6 Hz range, for observation of
3-mode optoacoustic interactions in a compact table-top system. Our design
incorporates an isolation stage and minimizes the acoustic loss from optical
coating. We observe a quality factor of 7.5 x 10^5 for a mode frequency of
401.5 kHz, at room temperature and pressure of 10^-3 Pa. We confirmed the mode
shape by mapping the amplitude response across the resonator and comparing to
finite element modelling. This study contributes towards the development of
3-mode optoacoustic parametric amplifiers for use in novel high-sensitivity
signal transducers and quantum measurement experiments.

Instrumentation and Detectors;Optics