Dynamic Optics and Photonics
Adaptive Optics for Microscopy
The imaging quality of a high-resolution microscope is severely compromised when aberrations are present in the optical system. These aberrations lead to reduced signal level and degraded lateral and, more significantly, axial resolution. Often aberrations are introduced not only by misalignment of optical components in the microscope but also by variations in refractive index of the specimen itself. We are developing adaptive optics systems to overcome these limitations. We have implemented adaptive optics in a range of microscopes and have demonstrated the benefits of aberration correction, showing improved contrast and resolution when imaging deep within specimens.
Many applications of our high resolution microscopes are in the biological sciences. Our research includes advances in the technology of confocal and two-photon fluorescence microscopes, harmonic generation microscopes and other high resolution methods. Applications have included cell biology, developmental biology and neuroscience. Through collaboration with colleagues in the Centre for Neural Circuits and Behaviour, we have particular interest in advancing optical methods for the investigation of neural activity in fruit fly brains.
Superresolution microscopy - or nanoscopy - enables visualisation of objects much smaller than the physical diffraction limit of light. These methods are regularly used in biological applications to resolve features in the tens of nanometres range. We are working on new methods for nanoscopy and in particular on the development of dynamic optics to extend the usability of this approach in practical applications. Our work includes technology and applications for stimulated emission depletion (STED) microscopy, single molecule switching methods (such as STORM, PALM, GSDIM) and structured illumination microscopy.
Adaptive Laser Fabrication
The high intensity in a tightly focussed laser beam can cause material modification that is well confined within three-dimensions. This provides the capability of fabricating 3D structures within transparent substrates. However, this usually requires focussing into high refractive index materials, which leads to significant aberrations that distort the focus. Since the size of fabricated features depends upon the shape of the focus, aberrations must be corrected for precision to be maintained. We are developing adaptive optics for the measurement and correction of these aberrations for machining applications.
Dynamic Parallel Laser Machining
Many direct laser writing systems rely upon the sequential exposure of the workpiece in a point-by-point fashion. This permits high precision fabrication, but at the expense of long processing times, especially when working in three dimensions. We have developed dynamic optical methods, using liquid crystal spatial light modulators to parallelise the laser writing process by creating multiple, individually controllable foci. This has been combined with aberration correction to maintain precision throughout a three-dimensional structure.
Diamond is an important material with many properties that make it useful across a wide range of engineering and scientific applications. We are developing methods for the processing of diamond and various applications ranging from quantum optics to biological sensing. In particular, adaptive optical laser fabrication methods enable the creation of structures deep within diamond crystals, including graphitic conductors. We are also using crystallographic defects, such as the nitrogen-vacancy colour centre, as electromagnetic sensors for detection of neural activity. This is a particularly powerful method when combined with super-resolution microscopy.