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Development of coherent X-UV laser sources

1 - Optical Field Ionisation collisional scheme
(B. Cros, G. Maynard, B. Robillart, A. Boudaa, K. Cassou, in collaboration with the group of S. Sebban at the LOA)

 Breakthroughs have been achieved in collaboration with the group of S. Sebban at the LOA-Palaiseau on X-UV laser sources created by laser ionisation of xenon and krypton gas. We have demonstrated experimentally that laser guiding inside a capillary tube allows to increase substantially the quality of the X-UV laser and of its energy as shown in Figure 1.

slpx_graph1 Figure 1: Measured amplitude of the X-UV signal as a function of xenon pressure at the output of a cell of length 16mm (squares), of a capillary tube of length 16mm (dots), of a capillary tube of length 30mm (triangles), and of a capillary tube of length 25mm (open circles).

 An important technical issue has been solved: capillaries with thick walls proved to be more robust and live through more than a thousand high energy shots, which is crucial for applications of capillary tube guiding.
The ITFIP group has also contributed to the development of a new diagnostics with sub-picosecond resolution of the time evolution of the gain of the source, based on the injection in the plasma of a pulse resulting from high order harmonics generation in a separate gas target [183].
Tests of injection of an harmonics beam into the amplifying medium contained inside capillary tubes have been performed. A large amplification, larger than 600, has been achieved when the harmonics beam generated in an argon gas cell and close to 32 nm, was injected in a capillary tube filled with krypton gas; future work will be dedicated to the systematic study of the parameters governing the amplification. These sources exhibit extremely interesting features for future applications: high repetition rate, high energy level and extremely good spatial and temporal coherence.

  The ITFIP group contributes to the experimental realisation and brings a strong support to experiments through theoretical work and modelling. An unexpected theoretical result was obtained: it was shown that strongly correlated plasma effects had to be taken into account to determine the ion temperature of the amplifying plasmas [50]. These predictions have been confirmed by molecular dynamics modelling performed by F. Lambert. A great deal of modelling effort, including the work of 2 PhD students, A. Boudaa and B. Robillart, and a collaboration with J. Dubau from the Lixam-Orsay, has resulted in the numerical code COFIXE which can be used for direct and quantitative comparisons between theory and experiment.

2 - Inner-shell pumping
(B. Cros, K. Cassou)

  A new scheme of X-ray source is being studied, in collaboration with S. Sebban and A. Rousse from LOA-Palaiseau and S. Jacquemot from LULI-Palaiseau, funded by the ANR from september 2007. This project, based on inner shell pumping of neutral atoms by a betatron source generated inside a capillary tube, should lead to the achievement, on the short term, of the first X-ray laser at angstrom wavelength.

3 - References

[50] G. Maynard, F. Lambert, N. Andreev, B. Robillar, A. Boudaa, J. Clerouin, B. Cros, A. Lenglet, T. Mocek, and S. Sebban, Determination of the Ion Temperature in a Plasma Created by Optical Field Ionization, Contrib. Plasma Phys. 47, 352 (2007)
[183] T. Mocek, S. Sebban, G. Maynard, P. Zeitoun, G. Faivre, A. Hallou, M. Fajardo, S. Ka-zamias, B. Cros, D. Aubert, G. de Lacheze-Murel, J. P. Rousseau, and J. Dubau, Absolute Time-Resolved X-Ray Laser Gain Measurement, Phys. Rev. Lett. 95, 173902 (2005).


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