The polarization characteristic of light is mainly determined by the complex refractive index of the target material, which is the fundamental cause of the polarization characteristic. The complex refractive index of the target material should be studied and measured first. In this paper, the reflectivity spectrum of the target material (the target material is mainly divided into metal and non-metal). Due to the influence of system noise measurement, the measurement of reflectance spectrum exist obvious ups and downs, in order to avoid the error influence on subsequent research, first of all, to get experimental data, based on the experimental data fitting, get rid of the noise be shaking experimental data, the data as the initial value. Then, different models are selected according to the properties of the materials, and a genetic algorithm is used to invert the model values. According to the experimental results, the measured metal experimental reflectivity spectrum jitter is obvious, so to correct the inversion, combined with the Kramers-Kronig relation, the complex refraction index is inverted. Finally, the inversion results of the two materials are compared with the experimental values, and the results are analyzed. The results show that the experimental values are in good agreement with the inversion values, which provides a theoretical basis for the subsequent research on the polarization characteristics of the target material.
The application of optical heterodyne detection is very demanding, and the roughness of target surface will seriously affect the echo heterodyne detection. In the study of electromagnetic scattering of rough target, Kirchhoff approximation method (KA) is suitable for studying the situation of small rough surface fluctuation. Through studying the laser scattering characteristics of target surface, it can be found that it plays an important role in the extraction of rough target characteristics, detection and acquisition of target echo data. Based on the experimental theory and electromagnetic scattering theory, this paper explores the influence and rule of rough surface on detection, verifies the correctness and feasibility of experimental theory by comparing and analyzing the results. It can be seen from the simulation results of heterodyne echo phase difference that the distortion in front of the detection return wave and the "decoherence" effect of intermediate frequency signal are mainly caused by the root mean square height and correlation length of rough surface. Simulation results based on the two theories show that, with the increase of roughness, the two signal values decrease sharply and then tend to zero; with the increase of correlation length, the two signal values increase first and then tend to be stable. The correctness and feasibility of heterodyne experiment theory are verified by comparing and analyzing the two simulation results.
In order to obtain the Mueller matrix of metal target, a model for measuring the Mueller matrix of metal surface is proposed in this paper. The model consists of light source, polarizing system, detecting system and detector. The Mueller matrix of any reflection direction can be measured in the plane composed of incident direction and target normal. The polarization modulation of light is realized by double wave plate rotation method. The Mueller matrix of metal target is inversed by discrete Fourier transform. In this paper, copper and aluminum are measured. In order to reduce the influence of error on the measurement results, this paper adopts the least square method to process the data. By comparing the experimental results with the model calculation, the results show that this method is an effective method to measure the Mueller matrix of metal targets. At the end of the paper, the advantages and disadvantages of the experiment and suggestions for improvement are given.
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