Polarization Effects In Large Aperture Laser Systems With Return Wavefront Sensors

Abstract

The performance of a large aperture, high energy laser system with a return wavefront sensor is dependant upon the correct measurement of the beacon wavefront and the resultant phase conjugation of the high energy laser (HEL) beam. However, high reflectance MLD coatings required for HEL systems can introduce polarization changes to the laser beams and wavefront phase errors since the wavefront phase errors can be wavelength dependent. Polarization selective sensors, such as interferometric wavefront sensors, may encounter large variations in intensity across the aperture due to the variation of the polarization state across the aperture. A significant uncorrected wavefront error may result when the beacon and HEL wavefronts differ due to the coatings and the incident polarization state of the beam. Estimation of the wavefront errors introduced into the beacon and HEL beams by the standard coatings is presented. An approach to reduce the intensity variations and wavefront differences is suggested and examined.