Ann Roberts - Research Interests
				Near-field scanning optical microscopy (NSOM)has become a widespread tool in biological and physical imaging. Aperture based NSOM relies on the use of a tapered optical fibre probe. These probes are usually coated with metal leaving an aperture with dimensions as small as 50nm at the tip. This tip is then scanned very close to the structure of interest and the object is either illuminated with light radiated from the end of the probe or light transmitted through or reflected from the structure is collected through the probe. In this way an image of the object with a resolution comparable to the size of the aperture is obtained. For over a decade now, we have been interested in extending these techniques to mapping both the intensity and phase of optical wavefields. In particular, we have produced precision maps of the intensity distribution near the foci of both high and low numercial aperture lenses. Recently, this work has been extended to studying phase singularities and we have observed both edge dislocations vortex-like structures at the focus of a lens. Another important application of this research is to the precision measurement of the mode structures within optical fibres and waveguides. From these measurements information about the fibre or waveguide, including losses and the refractive index profile, can be inferred. This work is currently being done in collaboration with researchers at Victoria University and together we are exploring a range of techniques, including NSOM, confocal microscopy and Differential Interference Contrast (DIC) Microscopy to the characterisation of a wide range of photonic devices central to developments in optical telecommunciations. Most recently, in collaboration with researchers in the University of Melbourne Conservation Service and the Ian Potter Museum of Art, we have commenced studies into the application of a range of novel imaging techniques to issues of importance in artwork conservation. These include the use of intensity-based phase imaging techniques pioneered within the Optics Group. Selected Publications: 1. D.J. Butler, K.A. Nugent and A. Roberts, Characterisation of optical fibres using scanning near-field optical microscopy, Journal of Applied Physics, 75, pp. 2753-2756, 1994. 2. A. Roberts and M.L. von Bibra, Fabrication of buried channel waveguides in fused silica using focussed MeV proton beam irradiation, Journal of Lightwave Technology, JL-14, pp. 2554-2557, 1996. 3. A. Barty, K.A. Nugent, D. Paganin, and A. Roberts, Quantitative optical phase microscopy, Optics Letters 23, 817-819, 1998. 4. S.K.Rhodes, A.Barty, A.Roberts and KA Nugent, Sub-Wavelength Characterisation of Optical Focal Structures, Opt.Commun, 145, 9-14, 1998.

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Created: 3 May 2001
Last modified: 3 May 2001
Authorised by: Head, School of Physics.

Maintained by: Ann Roberts, School of Physics.
Email: a.roberts@physics.unimelb.edu.au