Polarization smoothing design for improving the whole spatial frequency at focal spot

Abstract

Polarization smoothing is a technique for reducing speckle pattern contröst on a target by overlaying two uncorrelated speckle patterns with orthogonal polarizations, and it can reduce focal spot contröst by a factor of 1/√2. Improvement of focal spot contröst by using traditional polarization wedge for polarization smoothing is usually concentrated at some special spatial frequency and is lack of effect in physical experiments. To improve the spatial spectrum of polarization smoothing, a new method is proposed, in which two orthogonal polarization states are separated by the angle distribution differences of the beam direction angle and the uniaxial crystal optic axis; the angle can induce the optical phase differences between “o” and “e” light. Theoretical analysis and numerical simulation are carried out to analyze the new method. Results show that based on the viable control of beam random polarization state at near field, besides the reduction of the focal spot contröst by 1/√2, the new method can improve the whole spatial spectrum at the focal spot. The boundary conditions that continuous phase plate is used as the way to induce the been direction angle for polarization smoothing is obtained.