Study On Femtosecond Laser Modification And Chemical Etching Release Method Of Fused Silica Micro Hemispheric Resonator

Micro hemispherical resonant gyroscope(MHRG)is a kind of vibrating gyroscope based on Coriolis effect,and it is one of the core sensors of inertial navigation system.The resonant structure is the core component of the MHRG,and its manufacturing accuracy directly determines the performance of the gyroscope.The core technology of the resonant structure manufacturing is the high temperature forming and cutting release of the three-dimensional micro-hemispherical resonant structure.The release link of the resonant structure is to cut the resonant structure from the fused silica sheet.The high-precision resonant structure release process is a very important link in the resonant structure manufacturing process,and the surface quality of the resonant structure after release has a direct impact on the performance of the gyroscope.Therefore,the study of a high-precision resonant structure release process is of great significance to improve the performance of the gyroscope.In this paper,aiming at the release of high-precision micro hemispherical resonant structure,femtosecond laser modification and etching process is proposed for the release of fused silica micro hemispherical resonant structure,and an in-depth study is carried out to improve the surface quality of the cutting section.the main research contents are as follows:First,the mechanism of femtosecond laser modification and chemical corrosion of fused silica glass was analyzed.This paper briefly introduces the ionization mechanism and phase transition mechanism of femtosecond laser interacting with fused silica glass,and the three modification modes of fused silica material under different laser energy.it is found that the corrosion of laser-induced quartz to produce sub-wavelength periodic nano-grating is relatively high,which is more suitable for the cutting of fused silica glass.The technology of femtosecond laser modification and etching of fused silica glass is proposed.Second,the technology of femtosecond laser modification and etching fused silica glass mainly includes femtosecond laser modification process and chemical etching process,in which femtosecond laser modification process is the main factor affecting the cutting surface quality.therefore,this paper focuses on the femtosecond laser modification process of fused silica glass.A femtosecond laser processing system and an ultrasound-assisted chemical etching device are designed and built.The effects of two laser feed modes on the surface quality of quartz glass cutting section were analyzed,and then the effects of different processing parameters such as laser power,scanning speed and single feed on the surface quality of fused silica glass section were carried out.The optimized processing parameters are used to cut the fused silica glass.the edge collapse dimensions of the front and back of the cut are 1.6μm and 1.4μm respectively,the width of the notch on the front and back are 10.2μm and11.5μm respectively,the steepness of the section is 89.6°,the roughness of the section is 326.833 nm,and the corrosion selection ratio is 103:1.The cutting of fused silica glass with high precision is realized.Third,the reasons for the eccentric error of the resonant structure caused by the release process of the fused silica micro hemispherical resonant structure are studied.At the same time,the effects of the eccentric error on the natural frequency,frequency splitting and quality factor of the resonant structure are analyzed by using the finite element simulation software.The simulation results show that the eccentricity error will increase the natural frequency of the resonant structure,but has little effect on the frequency split.At the same time,the influence of eccentricity error on the thermoelastic damping is much less than that on the anchor loss,which will reduce rapidly.In order to reduce the influence of eccentricity error on the resonant structure,a femtosecond laser processing system with resonant structure is designed and built on the original femtosecond laser processing system of fused silica glass,which is used to eliminate the influence of eccentricity error,and finally successfully release the fused silica micro hemispherical resonant structure with good concentricity.Fourth,the natural frequency,frequency split and quality factor of the released fused silica micro hemispherical resonant structure were measured by using the built laser Doppler vibration measurement system.In the vacuum environment,the two natural frequencies of the working mode of the resonant structure measured by the frequency sweep method are1415.946 Hz and 14159.732 Hz respectively,the frequency split is13.786 Hz,and the quality factor Q measured by the attenuation time method is 391079.