Calibration method for geometric parameters of acousto-optic tunable filters based on polarization-dependent characteristics

The incident plane angle and ultrasonic cutting angle of AOTF affect the ray tracing inside acousto-optic crystals and AOTF spectral response characteristics. The results of accurate calibration of AOTF geometric parameters can be used as a preset input for the quantitative calculation of the spatial and spectral response of the AOTF imaging spectrometer system. In this paper, a method for calibrating the geometric parameters of medium-wave AOTF based on polarization-dependent characteristics is proposed. In this method, the tuning curves of the diffracted ordinary light (o-light) and extraordinary light (e-light) are measured when the incident laser beam is perpendicular to the input facet of the AOTF. Based on these data, the incident plane angle and the ultrasonic cutting angle of the AOTF are estimated using a least-squares fitting approach. It is unnecessary to rotate the AOTF device repeatedly during calibration. According to the calibrated AOTF geometric parameters, the center-tuned frequency drift of the two diffracted beams at different polar angles is calculated, and compared with the measured data, the experimental results show that the relative error of the center drive frequency can be controlled within 0.2%. This method is of great significance for the design of a mid-wave infrared AOTF spectral imaging system based on polarization multiplexing, image restoration of the spectral imaging system, and optimization of the spectral characteristics of AOTF devices.