Rotating a half-wave plate by 45°: An ideal calibration method for the gain ratio in polarization lidars

A new method is proposed to calibrate the gain ratio for polarization lidars in this paper, which involves a half-wave plate (HWP) placed immediately upstream of the polarizing beam splitter (PBS) in the receiver of polarization lidars. Gain ratio can be determined by rotating the HWP by 45° without key assumptions. The calibration results of this new method are independent of the monitored atmosphere as well as the system errors related to the components that are upstream of the HWP. Both theoretical calculations in the framework of the Mueller-Stokes formalism and experimental measurements are carried out to validate the calibration method.