Research on How Separation Angle Affects Focal Spot Polarization Characteristics in Birefringent Wedge Polarization Smoothing

Polarization smoothing (PS) can decrease the focused spot's intensity contrast, although its polarization characteristics may have a substantial impact on laser-plasma instabilities (LPI), such as cross-beam energy transfer (CBET). Based on a PS scheme using a birefringent wedge, this work statistically investigated the proportions of different polarization states within the speckles under varying separation angles. The findings show that the distribution of polarization states stabilizes when the beam separation angle is raised to 0.5×DL (diffraction limit) or above. Moreover, at a separation angle of 1×DL, no significant concentration of linear polarization was observed at the focal spot borders. The focal spot performs best overall at a separation angle of roughly 1×DL, according to the analysis of focal spot FOPAI curves. These findings provide a reference for further improving the application of PS.