During the past year, the main emphasis in this research program has been on multiphoton ionization spectroscopy of aromatic clusters. This is being pursued in addition to continuing work in areas of ion dip spectroscopy and ion fragmentation spectroscopy. The program has the overall objective of developing improved ultrasensitive molecular detection methods based on multiphoton laser spectroscopy. Photoionization techniques are employed due to their extreme sensitivity combined with mass selectivity. The combination of these two features has led to the current capability to study molecular clusters of specific sizes with high spectral resolution. Clusters are formed in abundance in a supersonic expansion, where they are excited and ionized by an ultraviolet laser beam. The studies reported here are principally based on simple resonant excitation of clusters, followed by one-photon ionization. For the naphthalene clusters, a single laser wavelength suffices for both excitation steps. Additional investigations have been carried out to measure excited state cluster ionization spectra and cluster ion fragmentation spectra. Results from these measurements are not yet sufficiently advanced to report in detail, however the preliminary data support the importance of recently proposed new fundamental ionization mechanisms in clusters. This brief report summarizes results described in more detail in …

The use of powerful microwave sources provide unique opportunities for novel and efficient heating and current-drive schemes in the electron-cyclotron and lower-hybrid ranges of frequencies. Free- electron lasers and relativistic klystrons are new sources that have a number of technical advantages over conventional, lower-intensity sources; their use can lead to improved current-drive efficiencies and better penetration into a reactor-grade plasma in specific cases. This paper reports on modeling of absorption and current drive, in intense-pulse and quasilinear regimes, and on analysis of parametric instabilities and self-focusing. 16 refs., 2 figs.

The output from a laser-driven high-fain ICF target in the laboratory microfusion facility (LMF) target chamber could produce enough x-rays, shrapnel, and debris to severely damage the laser's final optics. If the final optics were left unprotected, the replacement and reinstallation costs for each beam would exceed $40K. Assuming the laser has 68 beams, the replacement costs for each shot could reach $2.7M. To avoid these excessive costs, we must design a reliable optics protection system. This requires that we define the hazardous environment to which the optics are exposed. The geometrical layout for the 68 beams of the 10 megajoule laser shows the final optics placed at 25 meters from the target. The final optic will be a 2--5 cm thick debris shield ($40K each) which will be placed in front of a $200K focussing lens. Each of the 68 beams will deliver 150 kJ of 0.35 ..mu..m (3..omega..) light and will consist of either a 4 /times/ 4 or a 2 /times/ 8 array of beamlets, with each beamlet aperture having dimensions of 29 cm /times/ 29cm. This produces a 3..omega.. energy density at the final optic of 12J/cm/sup 2/ average and 225-30J/cm/sup 2/peak. 8 refs., 4 figs., …