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We have begun a program to measure dielectron production in /^-nucleus and nucleus-nucleus collisions at the LBL Bevalac. Results are presented for the reaction /? + Be at 4.9 GeV. For the first time, direct dilepton production is observed below 10 GeV incident energy. The cross sections are discussed and compared to previous data at higher energies. The observation of a structure at a mass of about 275 MeV suggests that pion annihilation may be the dominant production mechanism in this mass range.

energy, single-mode, narrow-linewidth fiber laser source using stimulated Brillouin scattering beam cleanup. Optics Express, Optical Society of America, 2007, 15 (10) Abstract:We propose an original nonlinear beam cleaning fiber laser architecture to obtain high energy pulses with a good beam quality and a narrow linewidth. The output beam of a large core Er:Yb co-doped multimode fiber amplifier (M 2 ~ 6, 220 µJ) is converted into a near diffraction limited beam (M 2 = 1.6) through a stimulated Brillouin scattering injection seeded beam cleanup process. We report in this experiment a multimode to single mode conversion efficiency of 50% while preserving the master oscillator linewidth.

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