The Ultrafast X-ray group works on the generation and uses of XUV and soft X-ray radiation using high energy femtosecond laser pulses. The X-rays are produced using high harmonic generation, a process which uses electron ejection and recombination to produce very short (attosecond) pulses of light.
Calculation of the electron density of a simple atom during the high harmonic generation process
Soft X-ray radiation has many important uses. Its short wavelength makes it ideal for high-resolution microscopy. Many chemicals have absorption edges in the soft X-ray region, making it an important area for spectroscopy.
Finally, the time resolution available from the generated pulses gives us the overall possibility of femtosecond time resolution and nanometer spatial resolution within the same instrument, which opens up whole areas of exciting new science.
The research effort in this area is multi-disciplinary. Within the ORC we collaborate with theory experts such as Dr Peter Horak, and in development of new femtosecond sources (Jon Price, David Richardson) .The group has a strong collaboration with the School of Chemistry, where X-ray scattering using more traditional sources is a long-standing and prestigious research area (the national centre for X-ray crystallography is based in Southampton Chemistry). More recently, we are building collaborations with the Institute for Life Sciences in the area of biological imaging.
Key to the process of soft X-ray microscopy is the use of phase retrieval techniques in imaging. These are computer algorithms that allow us to generate an image without the use of an objective lens. The scattered light from the illuminated object is collected, and the phase information necessary to recreate an image of the object, lost during the collection process, is recreated using an iterative algorithm. These techniques are extremely powerful, and will become very important in all forms of microscopy. We are collaborating with the School of Mathematics (UoS) and the University of Sheffield in applying these techniques to soft X-ray microscopy.