Preparation and controllable tuning of a high-quality factor phonon-laser in the optomechanical microsphere cavity

Low-threshold, narrow linewidth phonon lasers can greatly improve the detection resolution of sensors and have enormous potential for development in classical and quantum sensing fields, as well as information processing. However, its development is limited due to unfavorable factors such as the complex process, low quality factor (Q-factor), difficult tuning, and harsh environments requirements. Here, we report an easy-to-excite phonon laser with an ultra-narrow linewidth in silica whispering gallery mode microsphere optomechanical resonators at room temperature and ambient pressure. The microsphere cavity is fabricated by high-temperature melting with a CO2 laser and designed by controlling the proportion of the sphere to the stem (sphere-to-stem ratio) to reduce mechanical damping. By using a single-frequency laser as the pump source, the microsphere optomechanical resonator exhibited multiple breathing mode phonon lasers with ultra-high optical Q-factor (1.78 × 109), mechanical Q-factor (3.1 × 107), and low threshold (2.4 μW). It is the first time to achieve such a high mechanical Q-factor in the microsphere cavity system of this kind to the best of our knowledge, which opens up an avenue to develop highly sensitive sensors.