M. Perdrix

Bessel beam transformation by anisotropic crystals

Transformation of Bessel beams by biaxial and uniaxial crystals is investigated experimentally and theoretically. Experimental observations show beam symmetry changing and formation of complex intensity patterns, depending on the orientation of the crystal. These patterns can appear as a regular system of peak intensities. Results of numerical calculations support the experimental findings.

Xe(L) x-ray emission from laser-cluster interaction

We have measured absolute L x-ray emission yields from (Xe)n clusters (with n in the range 10^5 – 10^7 atoms/cluster) irradiated by 60 femtoseconds 800 nm IR and 160 femtoseconds 400 nm UV laser pulses of 10^15 – 10^17 W cm-2 peak intensity. Measurements have been performed as a function of cluster size (backing pressure) and laser peak intensity. Identification of spectroscopic features as well as x-ray emission yield variation with laser wavelength and intensity are in strong contradiction with results and interpretation from previous studies.

Role of the laser wavelength in the X-ray production for clusters under intense laser pulses

In case of laser-rare gas cluster interaction, precise evolution of the intensity threshold in the keV X-ray production with pulse duration has been determined at 400 and 800 nm. These measurements demonstrate that doubling the laser frequency does not increase the efficiency of the X-ray yield per cluster.

Sub-100 nanometer lensless probing of Co/Pd magnetic nanodomains using a table-top femtosecond soft X-ray harmonic source

We present recent developments of our table-top femtosecond high flux harmonic beamline towards single-shot probing of magnetic nanostructures. High harmonic generation (HHG) optimization in a single and two-color infrared laser pulse mode was investigated at high laser energy. Up to 109 photons per harmonic are generated between 40 and 80 eV in a single femtosecond laser shot. These soft X-ray harmonic photons are employed to characterize at the nanoscale the magnetic network of Co/Pd multilayer samples using resonant small-angle X-ray scattering. Selecting harmonics in the vicinity of magnetically dichroic absorption resonances of cobalt and palladium (Co M2,3 at 60 eV and Pd N2,3 at 51 eV) gives access to the magnetic nanodomain spatial structure. The magnetic scattering efficiency at the Pd edge is found to be comparable to that at the Co edge. This indicates that the Pd layers exhibit a significant induced magnetic moment. Magnetic sample optimization is then performed by characterizing its scattering efficiency as a function of layer composition and number of repetitions. We finally measure the spatial organization of magnetic nanodomains with a sub-100 nm spatial resolution from a single femtosecond X-ray pulse.