A set of materials—titanium, copper, and germanium—has been experimented with at the OMEGA laser facility [Boehly, Opt. Commun. 133, 495 (1997)] by irradiating thin foils with a prepulse prior to a main pulse with variable delay, in order to design efficient x-ray laser-sources for backlighting, material testing, and code validation. This concept led to increasing factors from 2 to 4 comparing to cases without prepulse, in the experimental conditions. As a result, high multi-keV x-ray conversion rates have been obtained: 9% for titanium around 4keV, 1% for copper around 8keV, and 2.5 to 3% for germanium around 10keV, which places these pre-exploded metallic targets close to the gas with respect to their performance, with wider energy range. A good agreement with hydroradiative code FCI2 [Schurtz, Phys. Plasmas 7, 4238 (2000)] calculations is found for titanium and copper on all diagnostics, with nonlocal-thermal-equilibrium atomic physics and, either nonlocal thermal conduction taking self-generated B-fields into account, or limited thermal conduction with intensity-dependent factor f. The results for germanium indicate that dielectronic processes could play a more significant role when higher irradiation intensity on higher Z material.

In the context of target design for multi-keV x-ray laser-produced experiments, the concept of exploding metallic thin foils by two laser pulses delayed in time has been tested at the OMEGA laser facility [J. M. Soures, R. L. McCrory, C. P. Verdon et al., Phys. Plasma 3, 2108 (1996)]. The first laser pulse creates an underdense plasma (ne∕nc≈0.2), and the second laser pulse heats the plasma plume which produces strong line emission from the titanium K shell (Heα at 4.7 keV and Hα at 4.9 keV). Six OMEGA beams (500-ps duration) for the prepulse and nine beams (1-ns duration) for the heating pulse irradiate one side of the foil. Different experimental conditions have been investigated in order to optimize the conversion efficiency enhancement on titanium foils. The influences of the foil thicknesses (5 and 6 μm), the delays (3, 4, and 5 ns) between the laser pulses, and the laser intensities (1.3 and 2.2×1015Wcm−2) have been tested. The absolute output power was measured by a set of filtered x-ray diodes, giving conversion efficiencies (CEs) up to 3.6% in 2π for energies above 4 keV with a preformed plasma, to be compared to the case without a prepulse where the CE is 1.5%. This double-pulse concept in this case shows an increase of CE by a factor of 2.4 for titanium thin foils. CE up to 4.9% has been reached with a laser intensity of 2.2×1015Wcm−2.

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The Laser Integration Line (LIL) is part of the Laser Megajoule (LMJ) project. The LMJ installation, which is of the National Ignition Facility (NIF) class, will deliver 1.8MJ at 0.35μm wavelength on target with 60 quadruplets of elementary beams. The energy on target of LIL is 30kJ corresponding to one quadruplet, it is housed in a separate building and has its own experimental setup. Target diagnostics have been progressively installed in the LIL target area. Energy and imaging diagnostics as well as the broadband and high resolution spectrometers have been fabricated in the frame of a unique industrial contract. Optical pointers are used to align the diagnostics to the target. The supervisory system controlling the diagnostics configuration and data acquisition is now able to manage cooperative and Commissariat à l’ Energie Atomique (CEA) shots. The calibration data base is accessible from the processing network and will very soon include the characterization of all the streaked, gated, and charge coupled device cameras. Only the Raman-Brillouin backscatter spectrometer still requires some final work and operating tests. The first diagnostics results have been obtained at the end of 2004. A gated soft x-ray imager, the Diagnostic de Mesure X (DMX) broadband spectrometer and a pinhole static imager were used in demonstration experiments. The purpose of the first experiment was to observe the closing of a slit etched in a tantalum oxide foam when irradiated by x-rays. The next diagnostics to be activated were the high resolution spectrometers, the gated x-ray imager, the two mirror x-ray imagers, and the scattered energy diagnostic. This was done during the preparation phase of a campaign realized in collaboration with the French Lasers and Plasmas Institute at the end of 2005 in order to study heat conduction in inertial confinement fusion plasmas. The next diagnostic which is now in preparation is a velocity interferometer system for any reflector. This diagnostic is in its fabrication phase and will be operational for diamond equation of state experiments.