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Synthesis of higher diamondoids by pulsed laser ablation plasmas in supercritical CO2The results on laser heating and ablation of graphite tiles of thermonuclear tokamaks are presented. Two pulsed Nd-YAG lasers ͑20 Hz repetition rate, 5 ns pulse duration and 10 kHz repetition rate, 100 ns pulse duration͒ were applied for ablation measurements. The ablation thresholds ͑1.0± 0.5 J / cm 2 for 5 ns and 2.5± 0.5 J / cm 2 for 100 ns laser pulses͒ were determined for the Tore Supra tokamak graphite tiles ͑backside͒ nonexposed to plasma. The high repetition rate Nd-YAG laser ͑10 kHz, 100 ns pulse duration͒ and the developed pyrometer system were applied for graphite heating measurements. Some unexpected features of laser heating of the graphite surface were observed. They were explained by the presence of a thin surface layer with the properties different from those of the bulk graphite. The theoretical models of laser heating and near-threshold ablation of graphite with imperfectly adhered layer were developed to interpret the experimental results.

We describe the principle of the polychromatic laser guide star(LGS) to recover the tilt information in imaging through the atmosphere. Observations using the A\TLIS laser at the Lawrence Livermore National Lab. are discussed in terms of returned flux in the ultraviolet. The major items of the programriie ELP-OA, starting now in France, are briefly reviewed, as well as the organisation of theLGS R&D in Europe. Finally the conclusion outlines the possible improvements of the polychromatic LGS to allows us to reasonably implement it at large astronomical telescopes.

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This study focuses on particles produced during laser ablation of a green colored acrylic wall paint, which is frequently used in industrial buildings and in particular in nuclear installations. Ablation is carried out with a Nd:YAG laser at a wavelength of 532 nm and a pulse duration of 5 ns, in a cell at ambient pressure and temperature, which is ventilated by filtered air. The number of particles emitted was measured with a Condensation Particle Counter (CPC) and their size with an Engine Exhaust Particle Sizer (or EEPS) for the nanometric range, and an AEROSIZER (for the micrometric range). The mass and shape of particles were determined by sampling on filters as well as on the different impaction plates of a Low-Pressure Impactor (LPI). Two particle populations were detected: a population of aggregates of primary nanoparticles with an electrical mobility diameter ranging from 30 to 150 nm, and a population of spherical submicron particles with an aerodynamic diameter ranging from 400 to 1000 nm. The spherical particles are mainly composed of titanium dioxide, and the aggregates most likely of carbon. The presence of two types of particles with different size distributions, shapes, and chemical compositions, implies that particles originating from the ablation of paint are formed by two different mechanisms: agglomeration in the case of the nanometric aggregates, which is preceded by

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.