Fig. 2
Pressure dependence of the WGM resonance frequency shift. a The pressure in the vacuum chamber is slowly increased from 17 Pa (olive) and 25 Pa (red) with 45 mPa s−1. The frequency shift is measured by counting the beat frequency at every second while the laser is stabilized to the WGM resonator by Pound-Drever-Hall locking. To confirm the frequency shift by the pressure change, the theoretically estimated lines from Eq. (1) for TM mode (dashed line) and Eq. (2) for TE mode (dotted line) are plotted together. The measurement values agree with the theoretical model within the 10% error bars agree with the theoretical model. For comparison, the 10% error zones of the theoretical values are added (gray). b The pressure in the vacuum chamber is increased from 17 Pa with 45 mPa s−1 (olive) and 130 mPa s−1 (navy), respectively. The measurements also agree with the theory within the 10% error zone of the theoretical values
