Probing electronic coherences by combined two- and one-photon excitation in atomic vapors.

Wave mixing in a three-level quantum system induced by two-photon resonant pump and one-photon resonant coupling at lower transition has been studied theoretically and experimentally. Resonantly enhanced difference-frequency generation efficiency was observed clearly dependent on the time delay and its sign between the femtosecond pump and probe. The role of the atomic coherences on the amplification without inversion during different sequences of interaction in a closed three-level system has been also stressed.

Supersonic cooling of rare-gas excimers excited in dc discharges.

Emission spectra of the homonuclear rare-gas excimers have been investigated in the wavelength region of 50 to 200 nm by using continuous discharges with supersonic jet expansion. The well-known dimer bands were readily observed in the emission spectra of He, Ar, Kr, and Xe along with an extremely weak band of Ne. A detailed examination of the Ar(2) band at 128 nm was carried out, and its envelope and bandwidth (8.

Efficient population inversion in excimer states by supersonic expansion of discharge plasmas.

Laser emission at 126 nm has been obtained from excimers of Ar(2) excited electrically in a nozzle discharge followed by supersonic expansion. The direct measurement of light amplification with a tunable VUV probe leads to a gain of >3 cm(-1). This high gain arises from efficient population inversion of low vibrational and rotational levels of the excimer state brought about by the supersonic expansion and cooling of the discharge plasma.

Radiative lifetimes of the B' (2)Delta state (v' = 0, . . . ,8) of NO obtained by vacuum-ultraviolet laser excitation.

Radiative lifetimes of rovibronic levels of the B', (2)Delta state of NO (from u' = 0,. . .