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Thèse/PhD | Study of ultra-fast laser matter - interaction by time resolved X ray diffraction

The aim is to optimize a hard X-ray source produced by the interaction of an ultra-intense laser (10 TW - 25 fs) operating at a high repetition rate (100 Hz) with a solid target for X-ray diffraction and imaging applications. In particular, the PhD student will study laser matter-interaction regimes that have so far not been explored to produce X-ray Kα (I> 1018W/cm2) and will carry out pump (optical) and probe (X) experiments to characterize the X ray pulse duration (<1ps) and to study ultra-fast laser mater interaction.

Starting date : October 1 – 2017 for 3 years.

Location : LP3 laboratory, Campus de Luminy –case 917, 13288 Marseille Cedex 9 – France

Contact : Marc Sentis (DR CNRS)

Funding : 1350 €/month for 3 years after selection of candidates based on an application form (April 2017) and an oral audition (May 2017).

Introduction and context of the PhD : Over the past ten years, new X-ray sources with a very short pulse duration (<10^-12 s) have been developed thanks to technological advances in high-power ultra-fast laser sources. The emergence of these X sources opens new horizons for ultra-fast and X-ray sciences. Applications are numerous and varied (solid and surface physics, plasma physics, femto-chemistry, biology, health, etc.). At LP3 laboratory, research on laser matter interaction is performed to improve knowledge, develop new applications and laser processes. More recently LP3 is also developing an ultr-fast X-ray source generated by the interaction of an intense laser pulse (Ilas> 10^16 W/cm2) with a solid target. This new secondary source is carried out in LP3 as part of the ASUR Platform ( A first PhD on this topic has been defended in october 2016, it was focused only on the X-ray source development at 10 Hz repetition rate. For the present proposed PhD the project will make the link between the characterization of the X-ray source and its application to study laser matter interaction with very high time and space resolution.

plateforme multi-TW ASUR

The PhD work will consist of three main tasks :

1) Optimization of an ultrafast Kα X-ray source obtained by the interaction of a Ti:Sa ultra intense laser (25 fs -10 TW) with a solid target at 100 Hz. This step can be carried out efficiently and rapidly by relying on a complete study already done at LP3 for a Molybdenum target at a lower repetition rate of 10 Hz . During this preparatory work, the PhD student will concentrate on optimizing two essential parameters for applications : the size of the Kα radiation source and the duration of the X-ray pulses.

2) Develop an original pump-probe diagnostic to measure the X-ray pulse duration. This measure remains a delicate point to be solved for laser plasma X ray sources and its outcome will be an important contribution to the scientific community. Indeed, the most powerful existing direct measurement tool such as straeck cameras are limited to pulse durations greater than 500 fs. An indirect method is to detect the change of an ultra-fast phase of material induced by an optical laser pump by X-ray diffraction. The PhD student will participate in the development of an ultra-fast (optical) pump and X-ray setup to caracterise the X-ray pulse duration ( 100 fs to 5 ps).

3) Study ultra-fast laser matter interaction. Knowledge of the ultrafast dynamics of the femtosecond laser interaction has increased significantly in recent decades, in particular by using pump - probe (IR - Visible - UV) experiments with a sufficient temporal resolution (typically 10 - 100 fs). However, fundamental questions remain open on the different processes involved in ultra-fast laser-matter interaction and predictive models are currently lacking. The problems are related to the difficulty of probing the matter not only at very short time scales, but also with a micrometric or even submicrometric spatial resolution to study the dynamics of the atomic lattice and the electron-hole plasma generated by laser irradiations. To carry out these studies, the doctoral student will adapt the pump-probe device (developed to measure the X ray pulse duration) to produce a time-resolved X-ray diffraction setup. Studies of ultrafast laser damage/modification mechanisms of materials like metals, semiconductors and dielectrics requiring analysis at time and space scales of interest ( ps and crystal lattice) will be carried out.

Keywords : material sciences, ultrafast phenomena, laser-mater interaction, instrumentation

Scientific skills : Physics, Optics, laser-matter interaction, material sciences and characterizations.

Personal skills : Experimental skills are mandatory, autonomy, curiosity, rigourus, good writting

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