Na, violet band excimer emission by electron beam excitation

There have been a considerable number of studies on alkali molecular diffuse bands concerning their excimertype nature.’ Such diffuse bands might be developed as possible sources of tunable, high-power lasers.2 Fluorescence of a Naa violet diffuse band could be observed either by one-photon excitation of X’c,’ w C’II, or two-photon excitation of an X’c,’ -+ A’C: -+ high-lying g state in Na,, or one-photon excitation of 3S-3P or two-photon excitation of 3S-4D in the Na atom.2-8 In particular, an observation of small signal gain in the violet band by 350.7 nm cw Kr + laser pumping has been reported.’ Recently, the upper states of violet band have been observed by Li et al. ‘o-” using optical-optical double resonance. As a preliminary step toward achieving a new tunable and high-power excimer laser in the violet, we presented the first observation of the Naz violet band emission by electron beam pumping. In addition, we also observed discrete spectral lines on the long wavelength side of the violet band. Although the analysis of these discrete lines is in progress, we tentatively assume that these lines represent the2’C,+ -. X’c$ bound-bound emission.‘3 The experimental setup used in the present experiment is shown in Fig. 1, which is similar to that previously described.14 The electron beam supplied by a Febetron 706 installed with a velvet cathode had a peak current of 4.5 kA, a beam diameter of 2.0 cm, a pulse width of 3 ns full width at half maximum (FWHM), and an electron particle energy of 500 keV. The electron beam, confined by an externally applied 1.5 kG axial pulsed magnetic field (nonuniformity less than 2%) passed through the anode foil, and a drifting section of 15 cm length filled with lowpressure helium and entered into a heat pipe oven containing dense sodium vapor, which was separated from the drifting section by a capton foil. The heat pipe oven had a diameter of 4.5 cm, a total length of 120 cm, and an active length of 60 cm, determined by the distance of the cooling coils. The emission from the active zone was introduced to a spectrum multichannel analyzer (SMA) through a MgF, window at the forward end of the cell. The resolution of the SMA system was 0.12 nm/channel with a 1200 graves/mm grating used in the 0.3 m spectrometer. The electron beam parameters were monitored by color foils and Faraday cups. About 50% of the peak current emitted by the diode was transmitted by the tube. The