An overview by Professor Keith Nugent FAA
The nursery rhyme 'Twinkle, Twinkle Little Star', the shimmer over a hot road and the network of bright lines at the bottom of a swimming pool on a sunny day all have their origins in phase. In fact, light is characterised by three main properties: colour, intensity and phase.
When light passes through a stained glass window its colour is changed. When light passes through a pair of sunglasses, its intensity (how bright it is) is changed. When it passes through a pair of prescription spectacles, the glass alters the phase of the light.
Many objects in nature are transparent. Obvious examples are air, glass and water, but think also of biological materials, eyes and, if you are 'seeing' with x-rays, even your aircraft carry-on luggage. Yet all transparent objects change the phase of the light - nothing is truly invisible to phase. It follows that any method that can 'see' phase can see things that are otherwise invisible.
Phase microscopy is a technique that has been around for a considerable time, with the first and most important development being due to the Dutch physicist, Frits Zernike, who received the Nobel Prize for this invention of phase-contrast imaging in 1953. Zernike's work was the first to allow a phase image to be seen. But the phase in the image could still not be measured.
I have spent much of my professional life trying to invent new ways of seeing things. For the most part, I have been looking at new developments in x-ray imaging and it was this work that led me to think about phase in a new way. With my colleagues and students, I set out to use my insights to develop new ways that would allow the phase in an image to be measured.
The obvious approaches to the problem turned out to be mathematically difficult and totally impractical. However, in 1998, with my student Dr David Paganin (now at Monash University) we developed an approach that seemed to have the promise of being simple, fast and very practical. With another student, Dr Anton Barty (now at the University of California), we showed that the methods could indeed be very effectively applied to optical, and then electron, microscopes. Their results were able to reveal - and measure - the phase in an image using clever calculations, but completely standard hardware. It was an extraordinarily flexible method.
The Paganin-Barty-Nugent technique has subsequently been used to also solve problems in x-ray, neutron and atom imaging. The international scientific interest in these new methods exploded and it rapidly became clear that the methods being developed by my team could be applied to a whole range of both practical and scientific problems.
We saw that this work had many commercial possibilities and so, with Drs Paganin and Barty, we took out a patent covering our new methods. This is the core patent licensed to Iatia Limited. Iatia has developed commercial packages for optical and electron microscopy. Iatia is now beginning to explore and develop the myriad other areas that can benefit from quantitative phase imaging methods.