Polychromatic measurement of the wavefront for high-contrast imaging with an MKID-based Pyramid Wavefront Sensor.

The Pyramid Wavefront Sensor (PWFS) is widely recognised as providing the best closed-loop performance for high contrast single conjugate adaptive optics (AO) systems, with many current and future AO systems selecting the PWFS as their primary natural guide star wavefront sensor. However, it is limited by its non-linear behaviour. Existing CCD/CMOS detector technology is well suited to PWFS operation, providing near-zero read noise detectors with frame rates of 1 - 3 kHz at either visible or near-infrared wavelengths. However, there is little scope for significant improvement in these detector technologies to further enhance PWFS AO performance and address non-linearities. In this thesis, we propose the use of a microwave kinetic inductance detector (MKID) array as an alternative PWFS detector technology and describe the benefits this can bring to future AO system performance. An MKID array is a superconducting detector with unique properties compared to CCD/CMOS detectors that provide a measure of the position, arrival time and energy of each photon incident on the array. Sorting the photons into wavebands allows us to measure the wavefront at multiple wavelengths simultaneously, providing additional information to overcome the limitations of the PWFS. In addition, photon counting becomes possible and new methods of reconstruction using temporal information can be explored. This thesis explore modelling methods and simulation results. It addresses the complexities of modelling PWFS systems that incorporate an MKID array, analysing wavefront at multiple wavelengths simultaneously, and proposing innovative strategies to mitigate non-linearities. As MKID technology is still in the development phase, it is important to understand its potential benefits for AO to guide the future development of arrays.