Synthetic aperture interferometry: measurement of steep aspherical surfaces using an anamorphic

Synthetic aperture interferometry (SAI) is a novel way of measuring aspherical optics (aspherics) where a scanning probe measures the optical path difference (OPD) between light reflected from the front (test) and rear (reference) surfaces of the aspheric optic. The surface form of the aspherical surface is subsequently computed assuming that the form of the reference surface is known. This-method is straightforward to implement, does not require null compensators and is inherently insensitive to vibration. Consequently it has the potential to measure aspherics as they are being polished. When SAI was originally proposed (Tomlinson, Coupland & Petzing 2003), bare fibres (NA - 0.12) were used to construct the probe, however this configuration was unable to measure steep aspherics and had poor light gathering efficiency. In this thesis, a new probe has been designed to measure the surface form of steep aspherics by increasing the NA of the probe using supplementary optics. In addition, the light gathering efficiency of the probe has been increased by adopting an anamorphical design. A single source and receive point of the probe was devised and it is shown that this configuration reduces the computational complexity. Alternative measurement configurations were investigated and their relative performance compared. A robust and fast phase evaluation process using a-priori information has been developed to extract the phase from measured interference pattern. Several steep surfaces have been measured to assess the feasibility of the SAI technique. Finally a detailed error analysis has been carried out to identify the major sources of error in measurement of OPD.