Adaptive optics for three-dimensional microscopy and photonic engineering

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Light is a versatile tool for imaging and engineering on microscopic scales. Optical microscopes use focused light so that we can view specimens with high resolution. These microscopes are widely used in the life sciences to permit the visualisation of cellular structures and sub-cellular processes. However, the resolution of an optical microscope is often adversely affected by the very presence of the specimen it images. Variations in the optical properties of the specimen introduce optical distortions, known as aberrations, that compromise image quality. This is a particular problem when imaging deep into thick specimens such as skin or brain tissue. Ultimately, the aberrations restrict the amount of the specimen that can be observed by the microscope, the depth often being limited to a few cellular layers near the surface. This is a serious limitation if one wants to observe cells and their processes in their natural environment, rather than on a microscope slide. I am developing microscopes that will remove the problematic aberrations and enable high resolution imaging deep in specimens.Focused light also has other less well-known uses. It can be used to initiate chemical reactions that create polymer or metal building blocks for fabrication on the sub-micrometre scale. These blocks, with sizes as small as a few tens of nanometers, can be built into structures in a block-by-block fashion. Alternatively, larger blocks of material can be sculpted into shape using the high intensities of focused lasers. These optical methods of fabrication show potential for use in the manufacture of nanotechnological devices. When manufacturing such devices, the laser must be focused through parts of the pre-fabricated structure. The greater the overall size and complexity of the structures, the more the effects of aberrations degrade the precision of the fabrication system. My research centres on the use of advanced techniques to measure and correct such distortions, restoring the accuracy of these optical systems.Traditional optical systems consist mainly of static elements, e.g. lenses for focusing, mirrors for reflecting and scanning, and prisms for separating different wavelengths. However, in the systems I use the aberrations are changing constantly. Therefore they require an adaptive method of correction in which the aberrations are dynamically compensated. These adaptive optics techniques were originally developed for astronomical and military purposes, for stabilising and de-blurring telescope images of stars and satellites. Such images are affected by the aberrations introduced by turbulence in the Earth's atmosphere. The most obvious manifestation of this is the twinkling of stars seen by the naked eye. Recent technological developments, such as compact and affordable deformable mirrors for compensating the optical distortions, mean that this technology is now being developed for more down-to-Earth reasons. This has opened up the possibility of using adaptive optics in smaller scale applications.In conjunction with researchers in Japan and Australia, I will develop adaptive optical fabrication systems that will be able to produce complex micrometre-scale structures with greater accuracy than was previously possible. With biologists in the University of Oxford, I will use adaptive optics to increase the capabilities of microscopes in imaging deep into thick specimens. This will enable biologists to learn more about the processes that occur within cells and the development of organisms. The aberration correction technology will also have use in other areas such as medical imaging, optical communications and astronomy.