Fundamental investigation of subsurface damage on the quality factor of hemispherical fused silica shell resonator

Hemispherical resonator gyroscope is an ultra-high precision and reliability solid-wave gyroscope. The quality factor (Q factor) is an important performance parameter of the resonator which is made of high purity fused silica. The subsurface damage (SSD) is generated due to brittle defects of fused silica during the grinding process. However, surface quality reduction caused by SSD significantly reduces the Q factor of the resonator. In this paper, the influence of SSD removal on the Q factor variation of the hemispherical fused silica resonator is investigated via the chemical etching method. The SSD depth of the hemispherical fused silica resonator fabricated by the precision grinding is measured. A device for Q factor measurement in high vacuum is built by employing the ring-down time method, which is composed of an impact exciter for excitation and a laser Doppler vibrometer for detection. The SSD is removed by chemical etching with several processing rounds. The Q factor and surface morphology of the resonator are evaluated after each round. The effect of residual subsurface damage depth on Q factor as etching processing is demonstrated. The experimental results indicated that the Q factor in the vacuum can be improved via chemical etching by 354% from the initial value of 1.84 × 105 into the final value of 8.36 × 105. The obtained results indicate that chemical etching can effectively remove the SSD on the subsurface of the fused silica resonator and significantly improve the Q factor.