Pyramid wavefront sensing: theory and component technology development at LAO

Pyramid wavefront sensors offer an alternative to traditional Hartmann sensing for wavefront measurement in astronomical adaptive optics systems. The Pyramid sensor has been described as a slope sensor with potential sensitivity gains over the Shack Hartmann sensor, but in actuality seems to exhibit traits of both a slope sensor and a direct phase sensor. The original configuration, utilizing glass pyramids and modulation techniques, is difficult to implement. We present results of laboratory experiments using a Pyramid sensor that utilizes a micro-optic lenslet array in place of a glass pyramid, and does not require modulation. A group of four lenslets forms both the pyramid knife-edge and the pupil reimaging functions. The lenslet array is fabricated using a technique that pays careful attention to the quality of the edges and corners of the lenslets. The devices we have tested show less than 1 micron edge and corner imperfections, making them some of the sharpest edges available. We finish by comparing our results to theoretical wave optic predictions which clearly show the dual nature of the sensor.