Polarization smoothing of large-aperture laser beams based on edge pressure induced stress birefringence

We report a method for achieving polarization smoothing of the large-aperture laser beam using a mechanical clamping device. A 450mm × 420mm × 43mm sized fused silica vacuum window was used as the implementation object for the polarization smoothing technique, and based on the narrow space constraints between this object and the high-power laser device, an implementation structure was designed that utilizes wedges to transmit and amplify loads. Under the action of the clamping structure, a gradient-varying planar stress field was generated within the optical aperture of the window, and the stress birefringence parameters of the material were altered, thereby realizing polarization modulation of the beam. Meanwhile, a near-field measurement device was designed for rapid offline measurement of the object's polarization modulation effect. The simulation and experimental results demonstrate that this method and structure can modulate a large-aperture linearly polarized beam into one with complex polarization state distribution, achieving a theoretical depolarization ratio of 40.8%. Moreover, this polarization smoothing method provides suppression of high-energy density speckle in the focal spot within the target area.