Polarized radiometry is an important means to obtain the physical state of astrophysical objects. The anisotropy of the light source or propagation path is the main mechanism leading to the generation of polarization. Therefore, polarized radiation can provide important information about vector fields such as the magnetic field or radiation field of astronomical objects. In the physics of solar measurement, using certain atomic spectral lines to measure high-precision polarized radiation is the main means to detect the solar vector magnetic field at present. When we measure the polarization of the solar magnetic field, two processes of polarization modulation and polarization demodulation are involved. The purpose of polarization modulation is to modulate the polarization signal into an observable intensity signal, which is mainly realized by the polarization analyzer. For different scientific objectives, the types of polarization analyzers are also different, and the polarization modulator either uses a rotating wave plate or controls a variable liquid crystal wave plate to realize polarization signal modulation. Polarization demodulation is the process of recovering the polarization signal from the observed intensity signal.When a rotating wave plate is used as a polarization modulator, it can be divided into a step modulation mode and a continuous modulation mode according to different rotation modes. The continuous modulation mode is widely used due to its high time resolution. At present, the "dual beam + continuous" modulation scheme is the mainstream polarization measurement scheme in the world. Therefore, this paper mainly studies the demodulation method in the continuous rotating wave plate modulation mode in polarization measurement. The main results and conclusions of the research are as follows:(1) Deduce the Fourier demodulation formula under the continuous modulation mode, use numerical simulation to simulate the demodulation process, compare the residual error between the demodulated signal and the input signal, and verify the correctness of the Fourier demodulation formula .(2) Use simulation to quantitatively analyze the demodulation performance of Fourier demodulation and matrix demodulation under the action of common errors in continuous modulation. The errors analyzed in this work include the initial azimuth error of the wave plate and the positioning accuracy error of the wave plate It is found that the demodulation performance of the two is basically the same, and the error range under the requirement of high-precision continuous modulation is given in the paper. In the process of demodulation performance analysis, the effects of wave plate retardance and modulation times on polarization efficiency are considered at the same time, and the optimized wave plate retardance and appropriate modulation times of continuous modulation are adopted.(3) A series of related actual measurements were carried out in combination with the laboratory adjustment of the FASOT polarization analyzer. The actual included angle between the transmission axes of the four polarizers in the calibration unit and the measured retardation of the purchased commercial wave plate are calculated by using the light intensity method.
修改评论