Développements de sources cohérentes X-UV pour les applications – ASOURIX
The ASOURIX project is proposed by a 4 young researcher team from Laboratoire de Physique des Gaz et des Plasmas (LPGP) and aims at developing laser produced coherent sources in the XUV domain with wavelengths between 10 to 20 nm. Those sources are soft x-ray lasers generated by the interaction of intense infrared lasers with solid targets and the high order harmonics generated in gas targets. They both constitute a very interesting alternative to synchrotron radiation thanks to their high brightness due to short pulse duration and great spatial and temporal coherence. The aim is to reach a high performance level for those sources, which will allow them to be used by external scientists coming from other fields of physics and biology and desiring reliable and easy-access source of irradiation and imagery. Up to now very preliminary and partial application results were obtained using those sources but due to lack of time, difficult access to large scale facilities and irregular collaboration with users they were more proof-of-principle demonstrations. They did not have real impact on the fields explored. We propose to take advantage of the 5 year old LASERIX facility of the Université Paris XI. It is based on high power infrared laser installation that can deliver up to 40 Joules in picosecond duration pulses at a repetition rate of 0,1 Hz. This radiation is then used to generate intense X ray lasers for applications requiring high energy or brightness in single shot experiments. In this project we want to use another infrared leak of the laser, which delivers pulses at higher repetition rate (10 Hz) and reduced energy (down to 2 Joule). Those beam characteristics allow, thanks to recent development made by the group, to produce high repetition rate soft x-ray sources with significant average power relevant for a large scale of applications. The ASOURIX project will thus develop two alternative beam lines at high repetition rate specifically dedicated to applications: the first one based on soft x-ray laser technology and the second one on high order harmonic generation. Having those two lines in parallel at the same wavelength but with different characteristics is really exciting: pulse duration is for example picosecond for the first line whereas it reaches the femtosecond even attosecond regime for the second one. The number of applications we want to develop is purposefully reduced to increase the level of performance and allow a regular and long-term collaboration with users teams. We want to collaborate with biologists team from LCAM (laboratoire des collisions atomiques et moléculaires) working on radiation induced single and double strand breaks of DNA using relatively low energy photons. The high level of DNA breaks induced recently by low energy photons is surprising if we compare it to the results of experiments using harder X rays. This means another process takes place that nobody can really explain for the time. We thus need a much larger set of experimental data to explore this new phenomenon. The biologists especially want to understand the role of integrated dose as compared to dose delivery: the question is if the same dose is more efficient if it is delivered in a shorter time. Those experiments will be carried out on our beam-lines using different pulse duration and wavelengths. Another important point is to understand the role of chemical catalysers of the irreversible destruction of DNA used for example in chemiotherapy and radiotherapy of cancer. A well known component is platinum but new efficient candidates seem to be metallic nanoparticles and their effect has to be tested. We will also collaborate with a research team from Laboratoire de Physique des Solides (LPS) on the production of the first non linear effects in this XUV wavelength range using soft x-ray lasers. This will only be obtained if the source has extreme brightness and is perfectly focussed to reach the very high intensity required for the observation of non linear effects. These experiments will allow a better understanding of the electronic structure of high technology materials such as high temperature supraconductors. Finally, we will develop pump-probe experiments such as time resolved interferometry at a picosecond and even femtosecond timescale and nanometer resolution connected to the short wavelength used. They will permit to characterize with unprecedented precision the evolution of dense plasmas or surfaces.
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