Ultrafast X-ray science

The dynamic properties of solids couple to atomic motion and the relevant time-scale is that of a vibrational period (~100 fs = 10^-13 s). This is the time scale on which molecular dynamics, chemical reactions and phase transitions in solids occur. In contrast with existing, fs laser probes, X-rays have a wavelength approximately equal to the distances between atoms, and hence enable atomic movements to be visualised directly. Thus, the natural technique for studying evolving atomic structures is through X-ray diffraction. Since their discovery, X-rays have been the dominant tool for determining atomic structures. We believe that the availability of time-resolved structural probes with sub-ps time-resolution which employ X-ray diffraction, would enable groundbreaking work by allowing the interrogation of rapidly changing structures. However, the lack of both ultrashort-pulse X-ray sources and ultrafast x-ray detectors has, until very recently, prevented such studies. During recent years a rapid development of pulsed X-ray sources has been achieved, falling into two main categories: Laser-based table top sources; and sources based on partice accelerations (e.g. synchtrotrons). Currently these activities are pursued in collaboration with research groups worldwide in order to utilise existing X-ray sources coupled to fs laser facilities. In the medium term (5-10 years), it is clear that the field will be driven by what can be achieved in terms of developing sources. Our work involves both source development and applied science.