Abstract

By two photon excitation of mercury vapor with a femtosecond KrF-excimer laser system (λp = 248. 5 nm) a variety of strong emissions in the near infrared, visible and vuv spectral range are observed, as indicated in Fig. 1. The coherent line emissions in the infrared (λ = 1µm - 2.6 µm), starting from the 10s and 10d levels, and in the visible (λ= 546nm, 436nm and 405nm) between the triplet 7s → 6p states, are due to amplified spontaneous emission (ASE) and stimulated hyper Raman scattering (SHRS) in the mercury atom. These emissions can not be observed in the interaction of nanosecond KrF-pump laser pulses with mercury vapor. Therefore it is assumed that the processes are resonantly enhanced by the high peak intensities of the pump laser system (up to 1*10^l5W/cm²), due to a level shift into the two-photon resonance by the ponderomotive potential. For the amplified spontaneous emission in the visible spectral range, pulse durations of about one nanosecond have been measured. Output energies of 20nJ are detected at a vapor pressure of 20torr.

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