We have made significant progress in developing the broadband X-ray source produced by laser wakefield accelerators for use in a powerful technique called X-ray Absorption Near Edge spectroscopy, XANES. XANES can provide detailed information about the temperature and structure of materials and the ultrashort broadband X-rays that we can produce using a laser wakefield accelerator are well suited to probing matter than is rapidly heated to extremely high temperatures and densities, of the kind that is found deep inside gas giant planets.
During the initial part of the grant we were able to record X-ray absorption spectra of a sample using a relatively low intensity X-ray source, but needed to integrate data over many shots to get a useful signal. Since then we have shown that we can do this in just a single laser shot, this makes it feasible to do studies where we watch how matter at extremely high temperatures (> 10000 ºC) rapidly evolves. We have also used the Gemini laser system to develop a new system for generating X-rays that can perform the heating. This means that we are now poised to make measurement of the rapid evolution of matter under extreme conditions using the dual beams of Gemini: one to produce the laser wakefield accelerators and ultra-short X-ray flashes and one to rapidly heat a sample to thousands of degrees.
We have developed an experiment that uses the electron beam produced by a laser wakefield accelerator to investigate the fundamental processes that occur in extremely high electromagnetic fields (such as might be found on the surface of a quasar). We have seen the first evidence of an electron losing energy when it collides with a very intense laser pulse, a process called radiation reaction and have seen hints that this behaviour can only be modelled using theories based on extreme electromagnetic fields. This work was published in two papers in Physical Review X and has received a lot of attention, with from the research community and outside.
We have successfully completed our first experimental run which aims to study how matter can be created when two photons collide. Our experiment uses our laser wakefield accelerator to produce high energy electrons, which are converted to high energy gamma rays. We then collide the gamma rays with a dense field of X-ray photons which are produced by shooting another high intensity laser at a think metal foil. As the gamma ray photons pass through the dense X-ray field then can collide with the X-ray photons and can produce pairs of electrons positions. Analysis of this run is ongoing so it is too early to say if we have observed photons colliding and creating matter, however all aspects of the experiment worked successfully.
