Study On Temperature Field Measurement Based On Laser Phase-Shifted Polarization Interference Tomography

At a time when informatics,optics and computer science are at cross-purposes,the ability to accurately measure the three-dimensional distribution of temperature fields is of great importance in aerospace engines,incubators for premature babies,the development of Micro-electromechanical Systems and advanced aquaculture,where the ability to accurately measure such temperature fields is a direct reflection of the performance of the device in question.As a non-contact measurement technique,optical chromatography has the advantages of high detection depth,no interference with the temperature of the measured area,and no harm or pollution.In this paper,a polarization optical laminar interferometry system is proposed to measure the three-dimensional temperature field distribution in the measured region.The measurement optical path is based on the Mach-Zender dual-beam interferometric optical path,and the light source is a dual-frequency He-Ne gas laser with P light as the measurement light and S light as the reference light.The P light is divided into P light and S light through polarizing beam splitter,and the P light is expanded as the measurement light path and then passed through the measured area,and then reflected by the all-reflective mirror after the beam is closed,and the S light is reflected by the all-reflective mirror as the reference light path,and the P light and S light are combined by the half-transmissive and half-reflective mirror and collected by the CCD.According to the experimental process,five interferometric images are obtained in turn,after which the multi-step phase shift calculation formula is applied to demodulate the phase difference.After obtaining the phase difference projection data of each projection angle,the three-dimensional refractive index distribution is calculated by the reduction algorithm,and then the three-dimensional temperature field distribution is obtained by the refractive index versus temperature formula.The feasibility of the measurement system is verified by simulation software,while an iterative exponential filtering back-projection reconstruction algorithm is proposed in this paper,and the reconstruction results are compared with those using conventional filtering back-projection and exponential filtering（EF）back-projection by normalizing the mean square distance and normalizing the mean absolute distance as evaluation parameters.the proposed algorithm has better reconstruction accuracy.The experimental system was built according to the optical circuit schematic,and the temperature field of the heat source was 150°C.The experimental results showed that the three-dimensional temperature distribution matched the actual situation,and the root mean square error was 0.30%and the average absolute percentage error was 0.226×10^-3%with the calibration temperature measured by the high-precision PT1000 high-precision platinum resistance temperature measuring instrument.The maximum difference between the two values does not exceed 2°C,and the maximum measurement system uncertainty is about 0.7°C.Therefore,this measurement method can be widely used in material testing,chemical composition analysis,medical diagnosis,environmental monitoring,microbiological testing and other related fields.