Study On Long-distance Vibration Measurement Method And Application Based On Laser Feedback Frequency-shifted Interferometry

Long-distance vibration signal detection is of great significance in the fields of machinery manufacturing,national defense and military.At present,the traditional vibration measurement methods and technologies cannot measure vibration of non-cooperative objects,and a mirror or a reflective film needs to be installed on the object,which limit the practical application of the system.Laser frequency-shifted feedback interferometry has the advantages of ultra-high sensitivity and easy collimation.It has outstanding performances in the detection of vibration signals of non-cooperative objects,but there are still problems such as short working distance,small incident angle,and weak feedback light intensity.In this paper,based on the laser frequency-shifted feedback interferometry,the solid-state microchip laser is used to gain the feedback optical signal intensity,and the long-distance vibration measurement method and its application research on remote sound reconstruction are carried out.The main research work and innovative results are:Research on solid-state microchip laser and its output characteristics and frequency-shifted feedback characteristics:The microchip laser is the core component of the vibration measurement system.It is designed from the aspects of pump source,gain medium,cavity length,and temperature control frequency stabilization,and realizes the steady-state output of the laser.The transverse mode,longitudinal mode,laser power stability,laser frequency stability and relaxation oscillation characteristics of the laser is analyzed systematically.The laser works in single longitudinal mode,and the long-term（4h）power fluctuation is 0.49%,and the laser frequency stability can reach 10^-7.The frequency-shifted feedback characteristics are simulated according to the rate equation,and the characteristics of the feedback signal strength and power spectrum at different feedback levels are experimentally studied.The analysis shows that the gain coefficient of the solid-state microchip laser can up to 10⁶,when the frequency-shifted frequency is close to the laser relaxation oscillation frequency.It indicates that the laser frequency-shift feedback has ultra-high sensitivity,and provides theoretical guidance for the construction of the subsequent feedback experimental system.Long-distance vibration measurement method and system construction:Aiming at the problem of long-distance non-cooperative object vibration signal detection,the long-distance vibration measurement method based on laser frequency-shift feedback is studied.The working principle of vibration measurement system is analyzed.The structural composition of the system is introduced from the optical system,signal demodulation,data acquisition,and then the measurement experiment system is designed and built.The uncertainty of the vibration measurement system is analyzed theoretically,including the air refractive index,laser frequency stability,system nonlinearity error and average phase error.The overall uncertainty of the system is estimated,and the overall system uncertainty is in the order of nm.Long-distance vibration measurement system performance test and analysis:The long-distance non-cooperative object vibration measurement performance test is carried out based on the construction of an experimental system.The results showed that the system accurately reconstructs the vibration waveform of the paper box 100 m away in the laboratory environment,and the frequency measurement error is within0.1%.The range of the incident angle of the beam can be up to±60°.In addition,the system can measure vibration of a variety of non-cooperative objects such as milk powder bag,polyfoam and so on,and it improves the actual application ability of the system,and can be well used in remote vibration signal detection.Long-distance vibration measurement system application test:Through the application test of long-distance voice reconstruction on non-cooperative objects such as paper boxes,the result shows that the system can clearly obtain single syllables and complex voice signals at 100 m distance.The range of the incident angle of the beam can be up to±60°,with high flexibility.The long-distance sound reconstruction based on laser frequency-shift feedback is achieved.The noise in the reconstructed audio can be eliminated effectively by using improved spectral subtraction.The research results lay the foundation for the system to be further applied to practical applications.