Concept for laser guide star dynamic refocusing using rotating phase plates

Laser guide star wavefront sensors (WFS) using pulsed lasers can benefit from dynamic refocusing techniques which synchronously adjust the focus of the wavefront as the light returns from the scattering layer so as to maintain a constant axial image location. Existing techniques involve pulsating discrete mirrors and high-speed segmented MEMS in the WFS path. A different approach is presented here, which uses a pair of rotating phase plates with cylindrical or Alvarezlens- style tracks near the WFS pupil. Rotational speeds and disk sizes similar to that used for compact disc operation are proposed. The plates can be manufactured by numerical machining of transparent plastic materials or as diffractive components.