Design of a broadband, high-power, off-axis spiral polarization reflector

Spirally polarized beams are known to produce a strong longitudinal field under high numerical aperture focusing. We report on the design of a reflective optical element with an off-axis geometry that is capable of transforming a uniformly polarized beam into a predominantly spirally polarized beam. By utilizing the retardance present in Fresnel reflection, our device can operate over a broad range of wavelengths. The output polarization and intensity structure of a beam passing through the reflector are calculated using polarization and scalar ray tracing. Vector diffraction is used to calculate the polarization and intensity structure under f/0.656 focusing. The off-axis reflective design is well-suited for high-power laser applications and could enable current and future laser-based particle accelerators to achieve strong longitudinal fields at focus.