Implementation of Visible Wavelength Adaptive Optics
at the William Herschel Telescope

Abstract

This thesis investigates visible wavelength adaptive optics for astronomy. More specifically, it presents the development High Order Adaptive Optics (HOAO) system CANARY-HOsted UpGrade for HOAO (CHOUGH) for the William Herschel Telescope (WHT). The CHOUGH is a narrow field of view high-order single conjugate on-sky Adaptive optics(AO) demonstrator designed to be implemented at the WHT.
The main focus of this thesis is the development of a High-Order Wave-front Sensor (HOWFS) and an Atmospheric Dispersion Corrector (ADC). A HOWFS is a central piece of this experiment; it is a Shack-Hartmann with a sampling of 31x31 subapertures across the pupil. The detector is a Nüvü EMCCD camera, operating at >500Hz. The lenslet array, collimator and relay are commercial off-the-shelf.
When observing at a wide range of wavelengths the atmospheric chromatic dispersion can limit the spatial resolution (Wynne and Worswich, 1986), and this limit cannot be overcome by the AO system unless it is equipped with an ADC. Usually to avoid pupil actuator-lenslet array mismatch, the ADC is customarily placed very close to the pupil plane. This design aims to achieve a non-pupil conjugated ADC suitable to be located in any place inside the collimated beam path; this is due to the restrictions given by CHOUGH optical relay. The ADC also needs to satisfy the very small pupil shift requirement,for pupil stability.
As the results obtained in the laboratory confirmed, both of these sub-systems have performed individually within their specifications which indicates that the proposed designs were successful.