Optimization Experimental Study Of Polarized Cavity Ring-down Technique For Measuring Stress Birefringence In Optics

In the process of preparing and applying of optics,it is necessary not only to meet the magnitude of very low absorption and scattering losses,but also to clearly grasp and control their stress characteristics.At present,the detection methods for stress include Stoney curvature method,nanoindentation method,and polarization modulator method,etc.However,with the development of high precision optics,these methods can no longer meet the demand for higher precision measurements.Therefore,a higher precision non-destructive detection technique for stress in optics is urgently needed.The polarization cavity ring down technique can further improve the measurement precision of stress due to the cumulative birefringence characteristics in the cavity,providing a new approach to this demand.In order to further improve the measurement precision of the polarization cavity ring down technique,this thesis conducts an optimization study in terms of decay mode filtering,signal acquisition and data processing,and measures the stress birefringence and loss characteristics of Si O₂ thin film samples.The main contents include the following:1.The stress sources of optics and the corresponding non-destructive stress detection methods are introduced.The application of polarization cavity ring down technology and the optimization research of optical cavity ring down technology at home and abroad are elaborated,and finally,based on the stress optics law,the stress birefringent resonant cavity response is deduced by using the Jones matrix round-trip model and the orthogonal dual-frequency interference model,which can derive the cavity birefringent phase difference size by measuring the oscillation frequency,and the measurement is not affected by the fluctuation of the light source,indicating that the polarization cavity decay technology is an ultra-high precision measurement method.2.A polarization cavity ring down system for measuring stress birefringence of optics was installed.It is observed that the decay time constant decreases randomly from a stable value to other values,causing a sharp decrease in measurement precision.By comparing the mean,standard deviation,and probability values of the decay time constant or reflectivity for the fundamental and higher-order modes before and after inserting a mode-matched single lens,changing the aperture diameter with adjustable size,and changing the set trigger threshold,it is concluded that the use of these three simple methods can reduce the measurement error of the decay time constant.And in practical measurements,the use of a mode matching lens in combination with a trigger threshold is a simple and easy method for improving the measurement precision of the decay time constant.Also,based on the relationship between the principal stress direction of the optics and the detector angle,it is concluded that the highest signal-to-noise ratio is obtained when the detector angle is located at an angle of 45°from the principal stress direction,and based on this conclusion,the detector angle can be optimized for the optics.Finally,the data processing aspect is optimized,and the acquired signals are averaged to make the obtained results more accurate and with less error.3.The effect of deposition angle on the stress birefringence and loss of Si O₂films was investigated with this system,the achieved measurement precisions were less than3.5 ppm for the optical loss and 5.0×10^-6 rad for the stress refringence,and the stress birefringence and loss characteristics of Si O₂ films with different deposition angles and the distribution trend of both with the change of deposition angle were obtained,which provided theoretical guidance for the preparation of thin films and proved that the polarized cavity ring down technique has a high measurement precision.