Aerosols are an important part of the global atmosphere and have a great effect on global climate change and human health. Polarization detection technology has important applications in the monitoring of atmospheric aerosols. Traditional polarization measurement instruments use the time-sharing measurement method to obtain the polarization information of the target by changing the relative positions of the analyzer and modulator multiple times. It is difficult to accurately determine the polarization information of the target by the time-sharing measurement approach when the target to be measured and the instrument are in the state of rapid relative motion. This study reports a polarization measurement method based on spatial amplitude modulation, which modulates the polarization information of the incident light to the spatial dimension through a polarization modulation module composed of a combo wedge and a polarizer. The module is combined with the dispersion module to disperse the incident light, and thus, the polarization information and spectral information of the target can be obtained simultaneously in a single measurement. In addition, the structure is stable without moving parts.

Firstly, the measurement principle of the system is introduced, and the modulation and demodulation equations of the system are derived. Then, the system's ability to distinguish incident light with different polarization states is demonstrated through the analysis of the demodulation equation, and the effect of the analyzer angle on the uncertainty of the measurement results is evaluated. After that, the effect of the amount of demodulated data on the overall modulation efficiency of the system is analyzed, and the effect of the analyzer angle on the modulation efficiency of Stokes parameters is evaluated. Finally, the system's calibration method of spatial and spectral dimensions is given, and the polarization measurement experiment is carried out with the system's principle prototype.

The uncertainties of the Stokes parameters Q and V reach the minimum value of 0.000124 at the analyzer angle of 15.9° and 74.1°, respectively, and the uncertainty of the Stokes parameter U reaches the minimum value of 0.00014 at the analyzer angle of 45° (Fig. 5). The overall modulation efficiency of the system is greater than 0.99 when the amount of demodulated data is greater than 130 (Fig. 6). The impact of the analyzer angle on the modulation efficiency of Stokes parameters is analyzed at the wavelength of 546.07 nm. The modulation efficiencies of Stokes parameters Q, U, and V reach the maximum values of 0.791, 0.662, and 0.841 when the analyzer angles are 15.9°, 45°, and 74.1°, respectively (Fig. 7). The effect of wavelength on the modulation efficiency of Stokes parameters is analyzed at the analyzer angle of 45°, and the modulation efficiency of the Stokes parameters U is always higher than those of the Stokes parameters Q and V in the wavelength range from 500 nm to 600 nm (Fig. 8). The experimental results show that the measurement error of the degree of polarization of the system is less than 0.060, and the measurement errors of the Stokes parameters Q, U, and V are less than 0.052, 0.035, and 0.057, respectively (Table 4). The measurement results illustrate the correctness of the theoretical analysis.

The article introduces the basic principle of the polarization measurement technique based on spatial amplitude modulation and gives the modulation and demodulation equations of the system. The system's ability to distinguish incident light with different polarization states is demonstrated through demodulation equation analysis, and the effect of the analyzer angle on the uncertainty of the measurement results and the modulation efficiency of the system is evaluated. An experimental device is built for polarization measurement experiments, and the system's calibration method of spatial and spectral dimensions is given. The experimental results are accurate to a certain extent and illustrate the correctness of the theoretical analysis. The work proves the feasibility of spectral polarization measurement technology based on spatial amplitude modulation. It is expected to be applied to atmospheric aerosol detection tasks in the future.