We report the photometric observation of a polychromatic laser guide star (PLGS) using the AVLIS laser at the Lawrence Livermore National Laboratory (LLNL). The process aims at providing a measurement of the tilt of the incoming wave front at a telescope induced by atmospheric turbulence. It relies on the two-photon coherent excitation of the 4D5/2 energy level of sodium atoms in the mesosphere. We used two laser beams at 589 and 569 nm, with a maximum total average output power of approximately 350 W. For the purpose of photometric calibration, a natural star was observed simultaneously through the same instrument as the PLGS at the focus of the LLNL 50-cm telescope. Photometric measurements of the 330-nm return flux confirm our previous theoretical studies that the PLGS process should allow us at a later stage to correct for the tilt at wavelengths as short as approximately 1 microm at good astronomical sites. They show also that, at saturation of two-photon coherent absorption in the mesosphere, the backscattered flux increases by a factor of approximately 2 when the pulse repetition rate decreases by a factor of 3 at constant average power. This unexpected behavior is briefly discussed.

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The multi-image framing camera based on gated MicroChannel Plates (MCPs), used in ICF programs, allows to ot*ain a sequence of two dimensional images in the x-ray range with gating times smaller than 100 ps and spatial resolution better than 20 p1/mm. After using such vices from different factories, we decided to lxüId our own tube. ir choice is motivated by the great fragility ofthe tube, consequent to both bad vacuum during the experiment and moisture due to frequent air 1aunching and by the mastery olthe technology which is necessary to rqxür rapidly such aratuses.The characteristics of the tube, particularly shutter time and spectral response, must be known as exactly as possible. Consequently we describe in these ges the method used to measure a shutter time ofabout 75 ps and we appraise the errors &e to the FWHM and the spatial unstability of the UV laser pulse employed to ifiuminate the front side of the MCP.The measurement of the spectral sensitivity, determined by experiments with synchrotron radiation on the storage ring SUPERACO in Orsay (FRANCE), shows a response in the energy band 2-5 keV different from the one measured with the gold vacuum-deposited photocathode on the MCP.

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In order to provide an accurate, repeatable reentrant plasma diagnostic support, an in-vacuum automated robotic diagnostic inserter (SID) was designed, built, and tested for the Phebus French laser facility. The SID system allows us to change quickly and accurately a diagnostic required for a new experiment. The other advantage of this new system is that the detector can be placed closer to the plasma (<0.5 m) and consequently the sensitivity of the corresponding diagnostic to x-ray photons or neutrons is increased. That permits more accurate measurements in present inertial confinement fusion (ICF) experiments (larger magnification ratio imaging systems with better spectral resolution). The SID has three major components: (i) a mobile platform which carries the diagnostic itself, (ii) a vacuum chamber, and (iii) an accurate mechanical guide system inside the target chamber. The repeatability of the diagnostic repositioning is at least ±10 μm over a travel range of 220 mm. Two main diagnostics are today in operation: a time grated x-ray imaging system and a high resolution crystal spectrograph. A detailed description of the main features of our SID and of two experimental results (implosion core formation imaging and spectra of x-ray argon filled microballoon) will be presented.