Study On Vibration Meatsurement Technology Of Laser Coherence Based On Acousto-optic Modulation

With the rapid development of science and technology,higher requirements have been put forward for vibration measurement technology in various industries,especially in the research and development of precision devices such as micro-electromechanical systems and data hard disk components,Vibration measuring instruments with good dynamic characteristics and nanometer resolution are indispensable.Laser Doppler interferometry,with the advantages of high resolution and non-destructive,has become the mainstream of modern vibration measurement technology research.In view of the current research situation of laser Doppler in China,which has low resolution and serious signal noise,this paper proposes a new vibration measurement technology of laser coherence based on acousto-optic modulation to achieve high resolution and high signal-to-noise ratio in engineering field measurement.Firstly,this paper studies the mathematical method of laser coherent vibration measurement,and establishes a mathematical model of two-channel laser coherent vibration measurement system based on acousto-optic modulation.The system uses the principle of laser Doppler measurement to ensure that the system has a high measurement resolution;through the design of laser interferometry structure,the anti-interference ability of optical path is improved;acousto-optic modulation is used to introduce a stable frequency difference in the range of 80MHz-120 MHz between the measured light and the reference light,which further improves the measurement resolution of the system.Secondly,after testing the performance of acousto-optic devices,the system chooses the central frequency of acousto-optic modulation to be 100.4MHz,and the diffraction efficiency reaches 88.9%,which improves the measurement resolution of the system.In view of the complex and difficult debugging of traditional optical path,the system introduces optical fiber to conduct transmission and develops an efficient optical fiber coupling system,which simplifies the optical path and improves the anti-interference ability of the system.Thirdly,in view of the fact that the signal output from the photodetector is very weak and the frequency components are complex,a step-by-step demodulation circuit suitable for the vibration measurement system is developed to improve the signal-to-noise ratio of the system;the fast Fourier transform algorithm is selected to transform Doppler frequency shift signal into frequency domain for analysis,and a combination algorithm of Zoom-FFT and ratio correction is proposed to solve the problem of low accuracy of frequency spectrum analysis after FFT,accurately extracts Doppler frequency and realizes vibration measurement with high resolution and high signal-to-noise ratio.Finally,the performance of the laser coherent vibration measurement experimental system is tested and the measurement uncertainty is evaluated.The experimental results show that the proposed two-channel laser coherent vibration measurement system based on acousto-optic modulation has a dynamic error of less than 1% in the frequency sweep test of 0.1 Hz to 4.5 kHz,and the measurement uncertainty is less than 0.6% at the frequency of 160 Hz and the amplitude of 80 um.Moreover,it shows a high signal-to-noise ratio and measurement resolution in the field measurement,which has a certain feasibility and practical significance.