A Hybrid Wavefront Sensor for Wide-range Adaptive Optics

Abstract

For centuries telescopes have been used to achieve an understanding of the universe and our place among it. As astronomical goals continue to push into infinite space for knowledge of the unknown, the instruments and mechanics must adapt to image farther and dimmer objects than ever before. To collect this information modern telescopes must grapple with the fundamental limitation imposed by the atmosphere. While more costly projects have begun to explore the option of launching smaller telescopes into space, the requirements for ground-based telescopes motivate an exponential increase in size and complexity. Larger apertures increase the sensitivity of detection, but the full resolution capabilities cannot be exploited without correcting the large and unpredictable aberrations imposed by the atmosphere. Adaptive optics seek to minimize these effects by applying an equal and opposite shape of the wavefront for correction. Wavefront sensors image incoming light such that phase aberrations are visible in the intensity field. The technique of this varies widely with application, but all wavefront sensors strive for high sensitivity, linearity, and accuracy over a large dynamic range. The proposed hybrid wavefront sensor builds from the well-established designs of the Shack-Hartmann and pyramid wavefront sensor, combining the ideal properties of both. Extensive simulations show that measurements from the hybrid wavefront sensor match the sensitivity of a pyramid wavefront sensor and the dynamic range of a Shack-Hartmann wavefront sensor. Two reconstruction methods estimate separate wavefront shapes corresponding to a highly sensitive or robust mode. These results provide a full understanding of the effect photon noise and initial aberration strength have on the hybrid wavefront sensor response. An adaptive optics testbench evaluates the hybrid wavefront sensor prototype, built primarily with commercially available optics. Single mode estimation tests show the linear response of both reconstruction methods. The initial results show high sensitivity when determining the mechanical non-linearity of the testbench deformable mirror. These laboratory tests support the simulated theory to show the hybrid wavefront sensor is adept at producing highly accurate wavefront estimations regardless of initial aberration strength. This advantage makes this sensor ideal for adaptive optics applications which require highly accurate corrections even in the presence of an unstable aberration source.