In this thesis paper the possibility of using Convolutional Neural Networks (CNN) for wavefront reconstruction is studied. This is tested with the Generalised Optical Differentiation Wavefront...Show moreIn this thesis paper the possibility of using Convolutional Neural Networks (CNN) for wavefront reconstruction is studied. This is tested with the Generalised Optical Differentiation Wavefront Sensor (g-ODWFS), a nonlinear pupil plane wavefront sensor that uses spatially varying polarisation rotators in the focal plane. Network architectures are developed for modal reconstruction in the Zernike and actuator basis. Both simulations and experimental work show that using a CNN for wavefront reconstruction improves the estimation of large phase aberrations as compared to the currently used linear method. This increases the convergence rate of the adaptive optics system, which is demonstrated in closed loop simulations.Show less
Spectropolarimetry is a versatile technique that allows an observer to measure both the spectrum of an object and the polarization of each point on that spectrum. Spectropolarimeters, like other...Show moreSpectropolarimetry is a versatile technique that allows an observer to measure both the spectrum of an object and the polarization of each point on that spectrum. Spectropolarimeters, like other spectrographs, generally use a slit to restrict their field of view to a line. However, slits have a long history of polarizing the light they transmit. Although multiple theories exist, and the polarizing behavior of slits near wavelength-scale is experimentally well-tested, the polarizing behavior of the generally wider spectrographic slits is less well-known and well-tested. We present a first step towards a new general model of the polarizing effects of slits based on waveguide theory and the eigenmode expansion that already shows the general expected behavior; linear polarization perpendicular to the slit’s long axis, as well as retardation effects with a similar perpendicular fast axis. Additionally, we tried to experimentally test the model’s predictions, but our setup proved insufficient. This was due to systematic errors, which could be removed using a different method, for which we provide suggestions.Show less
This thesis paper reports on the development of the Generalised Optical DifferentiationWavefront Sensor (g-ODWFS), a newly introduced wavefront sensor that relies on the polarisation of light to...Show moreThis thesis paper reports on the development of the Generalised Optical DifferentiationWavefront Sensor (g-ODWFS), a newly introduced wavefront sensor that relies on the polarisation of light to measure phase slopes and that may be well suited for applications such as high-contrast imaging. The wavefront sensor has been simulated through a computer model and its (broadband) performance has been analysed on the basis of sensitivity and dynamic range. Furthermore, a g-ODWFS prototype was designed, which has been successfully integrated in a high-speed closed-loop adaptive optics system in the lab.Show less
