Recent developments in X-UV optics and X-UV diagnostics

Metrology of XUV beams (X-ray lasers, high-harmonic generation and VUV free-electron lasers) is of crucial importance for the development of applications. We have thus developed several new optical systems enabling us to measure the optical properties of XUV beams. By use of a Michelson interferometer working as a Fourier-transform spectrometer, the line shapes of different X-ray lasers have been measured with a very high accuracy (/10^-6). Achievement of the first XUV wavefront sensor has enabled us to measure the beam quality of laser-pumped as well as discharge-pumped X-ray lasers. A capillary discharge X-ray laser has demonstrated a very good wavefront allowing us to achieve an intensity as high as 3×10¹⁴ Wcm^-2 by focusing with a f=5 cm mirror. The sensor accuracy has been measured using a calibrated spherical wave generated by diffraction. The accuracy has been estimated to be as good as /120 at 13 nm. Commercial developments are underway. At Laboratoire dOptique Appliquée, we are setting up a new beamline based on high-harmonic generation in order to start the femtosecond, coherent XUV optic . PACS 07.85.Nc;32.70.Jz;41.50.+h;42.15.Dp;42.55.Vc;52.70.La     

Photoionization of highly charged ions using an ECR ion source and undulator radiation

Photoionization of Xe4+ to Xe7+ ions was studied by combining an electron cyclotron resonance ion source with synchrotron radiation. Multiconfiguration Dirac-Fock calculations were performed to interpret the data. Many autoionization lines were measured and identified, resulting from excitation of a 4d electron into nf and np orbitals followed by Auger decay of the excited states. Continuum photoionization is negligible for the higher members of the isonuclear series.     

Longitudinal coherence measurements of a transient collisional x-ray laser

We present what is to our knowledge the first longitudinal coherence measurement of a transient inversion collisional x-ray laser. We investigated the picosecond output of a Ni-like Pd x-ray laser at 14.68 nm generated by the COMET laser facility at the Lawrence Livermore National Laboratory. Interference fringes were generated with a Michelson interferometer setup in which a thin multilayer membrane was used as a beam splitter. We determined the longitudinal coherence for the 4d1S0 --> 4p1P1 lasing transition to be approximately 400 microm (1/e half-width) by changing the length of one interferometer arm and measuring the resultant variation in fringe visibility. The inferred gain-narrowed linewidth of approximately 0.29 pm is a factor of 4 less than previously measured in quasi-steady-state x-ray laser schemes.     

An Air Permeability Study of Anisotropic Glass Wool Fibrous Products

This article reports an experimental study of the permeability of fibrous porous media based on air flow. Two glass wools have been analyzed in three different flow directions to evaluate their anisotropic structure. The usual flow theories such as Darcy’s law, valid for granular materials, have been shown to apply also to these fibrous media which is a more complex structure (fiber arrangement, high porous media,…). The intrinsic permeabilities and the anisotropic factors have been determined from an air permeability measurement based on a standard test for industrial fabrics. The experimental results have been compared to different models, showing the limits of some simplistic models when applied to our highly porous structures. One model, Kyan’s model based on the flow around submerged objects, was, however, found to agree with our experimental data. This study also demonstrates the interesting use of an experimental technique, which is air permeability measurement (water permeability is not adapted), in the investigation of flow phenomena in a fibrous medium.