Design and investigation of a four mirror scan engine incorporating parabolic reflectors

In this thesis, a novel optical design for an afocal scan engine based on two 90° off-axis parabolic optical elements acting as reflective relay optics between two deflecting mirrors is proposed. The characteristics of this scan engine such as linearity of scan lines, spot sizes, spot intensity profiles, field curvature, and temporal distortion across the scan field have been investigated. The new scan engine was also evaluated as an afocal relay, with scan optics and for optical zoom performance. The engine was modelled and investigated using OSLO, commercial optical software. Its performance was evaluated and compared to known scan engines with results showing superior linearity of scan lines and intensity distribution across the scan field. The advantage of using it with a fast resonant scan mirror is highlighted. The new scan engine prototype and known scan engines were assembled in the laboratory and their performance was evaluated and compared in order to verify the OSLO prediction. The experimentally measured results were found to be in agreement with the OSLO predicted results. A physical explanation for the difference in results has been provided. Using OSLO optical software, a study of temporal distortion across the scan field was then conducted. The calculated results predict that the use of the new scan engine in two-photon microscopy may result in improved contrast in two-photon images across the scan field. The new two-photon excitation correction factor for reflective scan engines was introduced and its evaluation confirmed that the new engine is the best choice for fast scanning two-photon microscopy (TPM).