Physics

Active Optics for Space Telescopes

Future Space Telescopes will be required to provide exquisite image quality, especially for such challenging tasks as the detection of extrasolar planets. The optics of these telescopes may be misaligned during launch, or through thermal effects, and it is essential to have a way to automatically measure and correct these errors. This is the purpose of Active Optics. In this work, we have proposed a 4m Space Telescope ('Hypatia') the image quality of which is constantly maintained by an active optics system. The system consists of a wavefront sensor and a deformable mirror. We are designing the system and building a laboratory prototype to demonstrate the required extreme accuracy and stability of the wavefront correction.

High-resolution retinal image processing

Adaptive optics is now used to provide images of the retina with unprecedented detail. Image processing can further enhance these images by selecting those images with the highest contrast, and precisely registering the images. We have developing ways to automatically detect photoreceptors (cones and rods) and nerve fivers in the retinal images and quantify the state of the cone mosaic. Quantification of these structures at high resolution will allow early detection of retinal disease, and tracking the effects of treatment. We are carrying out this work in close collaboration with ophthalmologists.

Computational Imaging

Computational imaging involves the combination of optics and image processing to enhance some aspect of imaging or allow the extraction of new information. For example, aperture masks may be designed which extend the depth of focus of a camera, or allow depth to be extracted from images. Plenoptic cameras and camera arrays provide information on the 'light field' i.e. the direction of the rays from the objects in the scene. This information allows digital re-focusing, the generation of synthetic views and recovery of 3D object shape. The gain in angular information is traded against spatial resolution, and we are investigating techniques to provide higher spatial resolution. This will be particularly important for applications in microscopy as well as macroscopic applications, such as face and gesture recognition.
 
Exoplanet Detection

A large number of planets have been detected outside our solar system using indirect techniques (e.g. see here). Imaging of these exoplanets is extremely challenging given how close they are to their parent stars, and how much fainter. The brightness ratio with the parent star is of the order 10^-6 to 10^-9. Obtaining such images will require using large (or extremely large) telescopes, with practically perfect adaptive optics. Even so, residual speckle effects severely hamper our ability to unambiguously detect exoplanets. We have developed optimal techniques based on using knowledge of the data statistics. We have also developed a powerful inverse-problem approach applicable to multi-wavelength data. This exploits the fact that the position of residual speckles scales with wavelength, and this fact may be used to discriminate speckles from planets. We want to extend these approaches to future Extremely Large Telescopes. 
 
Enhancing microscopy using Adaptive Optics and deconvolution

Images obtained with microscopes may be blurred by aberrations introduced by the sample. Adaptive optics has been used recently to correct for these aberrations and provide clearer images. Alternatively, the aberrations can be measured and the correction applied in post-processing. We are comparing these approaches in order to understand the relative benefits as applied to different modes of microscopy.

Thermal Imaging
 
We are investigating the combination of thermal and visual imaging for novel applications. The thermal imager has much lower spatial resolution than the visual camera, and we are developing techniques to 'fuse' the data from the two systems in order to enhance enhance the function. An example of application is the measurement of core body temperature from the nasal corner of the eye.

Current Teaching:

PH217:  Light, Atomic and Nuclear Physics
PH351 : Wave Optics
PH402:  Medical Image processing

Previous:

PH211: Electricity, Magnetism and circuits 
PH103: History of Astronomy
PH459: Applied Optics