Optics
Group leader
Professor Andrew Peele
Professor, Faculty of Science, Technology and Engineering
Diffractive X-ray imaging
Under certain conditions the diffraction pattern from a non-crystalline sample can be used to obtain information about the structure of that sample. We have recently shown that a number of advantages exist if the diffraction pattern is produced using curved beam illumination.
The goal of the research is to implement curved beam methods in experimental systems and to obtain high resolution images of objects that would not be possible using existing, plane-wave illumination methods. Ultimately we wish to apply these methods to samples such as cells and proteins that are not amenable to traditional crystallisation methods.
Phase imaging and tomography
A wide range of phase retrieval methods now exist under circumstances where the detected image of the object might be said to be only ‘mildly diffracted’. We have recently been funded by the Victorian State Government and the Australian Research Council to purchase a laboratory-based X-ray tomography system.
We seek to understand under which experimental conditions the various methods will be optimal for our system. This will lead to many applications in understanding the microstructure of materials for which it has been difficult to obtain direct 3D data. Examples include imaging the porous microstructure in structural metals, biological structures such as blood vessels in brains, and cracks in advanced materials such as laminates and carbon fibres.
X-ray vortices
A state of a propagating beam of light in which surfaces of constant phase describe a helical curve around the axis of propagation is characterised by a donut-like distribution in intensity in a plane perpendicular to the axis of propagation. Such a state is known as a vortex beam. Vortex beams are important at X-ray wavelengths as most phase imaging methods are unable to correctly recover the direction of the helical turns in the phase. In this work we aim to reliably produce high quality vortex states in X-ray beams and thereby test advanced phase retrieval techniques.
Diffractive optical elements
By correctly tailoring the structure and thickness in a mask the distribution of light in a beam that has propagated through the mask can be altered. The best known example when using X-rays is the Fresnel Zone Plate, which produces diffracted focal spots. However, a wide variety of patterns are possible, including X-ray vortices. We wish to optimise diffractive optical elements for a range of applications, including possibly X-ray lithography and providing structured illumination for diffractive imaging methods.
X-ray lithography
In X-ray lithography an X-ray sensitive resist is exposed through a patterned mask to an intense beam of X-rays. The resist is developed to produce a patterned structure which can either be the final device or be used as the starting point for further processing. This simple explanation belies the myriad of relevant parameters that can affect the quality or even the achievement of the final product. In this work we have concentrated on methods for producing extremely tall structures that are densely packed. Such structures have uses ranging from collimation grids to fluid transport devices and as a class of X-ray optics known as the lobster-eye lens.
Lobster-eye optics
An array of square channels (which happens to mimic the arrangement in a lobster’s eye) can be configured to bring an incident beam of X-rays to a type of focus. We have shown that such a device will operate as a particular type of X-ray telescope known as an all-sky monitor. An all-sky monitor based on lobster-eye optics offers unprecedented sensitivity and resolution.
An international consortium of institutions led by Leicester University is currently being supported by the European Space Agency in efforts to place a lobster-eye telescope into space. Our work has concentrated on modelling the performance of the space-based telescope and on investigating new methods for making the lobster-eye array.
