Freeform crystal optics for arbitrary space-variant polarization control in large aperture, high energy lasers

Abstract

High-average-power solid-state lasers are often severely limited by thermally induced stress birefringence, leading to depolarization losses and damage issues. Depolarization losses can be mitigated by selecting appropriate polarization optics to compensate the space-variant stress birefringence distribution. While some small-aperture, low-fluence technologies are available, no solution so far can provide a combination of high fluence and large aperture with a high degree of control of the beam quality.In this work, we demonstrate the use of magnetorheological finishing (MRF) technology to carve a prescribed thickness profile in a quartz waveplate to achieve precise space-variant polarization control. An arbitrary distorted polarization distribution can be converted into a uniform linearly polarized beam using two freeform MRF crystal optics with their crystal axes offset by 45 degrees. This technology is readily scalable to high-fluence, large-aperture applications, potentially enabling new regimes of laser operation.