Galiya Sharafutdinova

Improved field scanner incorporating parabolic optics. Part 1: Simulation

An unobstructed afocal scanning system design employing two off-axis parabolic reflectors as relay optics between two flat scan mirrors is proposed and investigated using OSLO optical software. It is found that, with a symmetric arrangement of the parabolic reflectors and appropriate selection of the first scan mirror rotational axis, the system provides linear scan lines at the image surface and excellent point spread function results in all scan positions. The design is functionally equivalent to a single-mirror scan engine and superior in every metric to a comparable dimension spherical mirror arrangement. This design is suited to two-dimensional laser scan engines and for confocal and two-photon microscopy in particular.

Improved field scanner incorporating parabolic optics. Part 2: experimental verification and potential for volume scanning

We investigated the experimental performance of an afocal scan engine employing two off-axis parabolic reflectors and it was found not to introduce astigmatism when compared to a freely propagated beam. The performance of the new afocal engine is very similar to an ideal single-mirror scan engine in terms of spot size and beam spot profile (or point spread function) and has an improved flatness of field over other two-dimensional laser scan engines. The parabolic scan engine is contrasted with a comparable spherical mirror arrangement and found to produce superior performance at the intermediate image plane when focused through a scan lens. Further modeling and experimentation point toward volume scanning applications. The significant performance improvement provided by this design, now verified experimentally, will result in superior image quality for fast scanning confocal and two-photon microscopy in particular.

Calculated two-photon fluorescence correction factors for reflective scan engines

Excitation laser spatial and temporal characteristics at the objective focal point are critical to the performance of two-photon scanning microscopes. Optical aberrations in scanning systems increase the microscope objective focal spot area and introduce pulse time broadening in the deflected beam, resulting in degradation of two-photon-induced fluorescence across the scan field. The geometrical pulse broadening is investigated for what is believed to be the first time and then combined with a focused spot area to provide a normalized two-photon fluorescence intensity correction factor. This factor, calculated using OSLO optical software, is compared for four reflective scan engines and allows compensation of the detected signal with position across the scan field. This new metric highlights that a parabolic mirror afocal relay exhibits superior performance as a reflective scan engine for two-photon scanning microscopy.

The volume scanner optical performance

The optical performance of a volume scanner is analyzed using modelling software. The existence of an embedded scattering volume with a 2.5% difference in scattering coefficient from the host media may be detected.

A volume scanner for diffuse imaging

Non-invasive optical screening mammography has a significant barrier in the extreme scatter of human tissue at optical wavelengths. A volume scanner suited for high numerical aperture capture of scattered light from diffuse media has been designed, modelled using Trace Pro software and experimentally constructed. Modelling results indicate the presence of an embedded volume with different scatter properties from the bulk yields a measurable difference in the overall scatter pattern and intensity recorded. Work towards a full tomographic reconstruction from scattered light recorded on the two dimensional array detector is currently underway.

A new volume scanner

Optical imaging through complex biological media remains a very challenging task due to the extremely high scattering experienced. A new design scanner is proposed and modelled which images scatter spatio-temporally. Modeling confirms the performance of the design. The inversion algorithm to reconstruct the scattering object remains as future work.

Off-axis parabolic optical relays: almost perfect imaging

Off-axis parabolic elements have found application in Tera-Hertz imaging and new application in two-photon microscopy scan engines. Both these applications demand spatial and temporal precision in photon location. This modelling work examines how close off-axis parabolic elements are to the perfect image relay by calculating the geometrical performance metrics of spot diagrams, point spread functions and wavefront distortion for different arrangements of off-axis parabolas and a parabolic torus when compared to a close-coupled two mirror scan engine. Results identify the off-axis parabolic elements as a superior scan engine particularly in wide-field scan instruments. When within the optimum beam size versus parabola focus length ratio, the imaging of these systems is superb.