The scientific program of this Centre is based around the capabilities offered by coherent x-ray sources. The coherent output of synchrotron sources, while high in comparison with more conventional sources, is still very low in comparison with a laser source; it is eight orders of magnitude below that of an X-FEL. It is critical that we are able to test short wavelength coherent techniques on a small scale before moving to larger sources.
We therefore propose to establish a program to develop coherent short wavelength sources based on recent developments in high harmonic generation x-ray lasers. The output will be in the form very coherent pulses of sub-picosecond duration.
The establishment of a short-wavelength laser program aligns the Centre program with the international X-FEL community and will position Australia at the forefront of ultra-fast X-ray technology in readiness for the forthcoming advent of X-FELs as well as modern development in third generation synchrotron sources.
The prime aim of this program will be the development of a coherent source of short wavelength, ultra-short pulses based on nonlinear optical processes. The Swinburne femtosecond laser facility can be upgraded to produce a source for the generation of XUV radiation and X-rays. This work will achieve a coherent output at less than 20 nm wavelength after the first year. In the next stage, a source will be developed for the generation of X-ray pulses in the water window range ( 4 nm), in line with the latest developments internationally.
In the longer term, we would hope to access the sub-nm wavelength range.
Once the first of these sources is operating we will instigate a program of imaging based research using coherent diffraction. The wavelength of the output will be much longer than that which will be required for the protein structural methods, but will be an intermediate step between current visible sources and future x-ray sources.
Imaging methods: The first goal of this project is to explore coherent diffractive imaging. The longer wavelengths of these sources will lead to substantial diffraction of the highly coherent light. We will use highly diffracting samples generated by the Experimental Methods Program and algorithms developed by the Theory and Modelling Program to develop robust and practical approaches with this method. Once these coherent methods have been demonstrated, we will use the Mn doped structures and amyloid fibril samples developed by the Biological Sciences Program to image live sub-cellular architecture with very high spatial resolution.
As the laser program can deliver ever shorter wavelengths, ultimately approaching the x-ray region, we will evolve higher resolution imaging systems. As the wavelengths enter the "water window" region, in which the wavelength is between about 4 and 2nm, the sample will develop the increased contrast expected from classical absorption x-ray microscopy. Morover, the full wavefield recovery allowed by our coherent methods will allow phase contrast and so additional contrast channels may become possible outside the water window region.
Dynamic structural investigations: The enabling technology of short pulse XUV/X-ray radiation generation unleashes the field of dynamic structural measurements. The Centre will also capitalise on this capability. We will adopt ultrafast pump-probe based spectroscopic and imaging methods, including "coherent" nonlinear spectroscopy, that have been established for visible wavelengths, for use in the XUV/X-ray regime. The ultrashort multiple laser pulses will induce a change in the molecular system and the molecular dynamics will be probed over a very broad range of wavelengths down to the X-ray region. Studies of the dynamics of biological molecules such as myoglobin, haemoglobin and related systems, as well as light harvesting molecules such as carotenoids and billiprotein, will be undertaken. The expertise of CIs Dao, Hannaford and Smith is invaluable in this aspect of the work.
