Optically pumped ring laser oscillation to vibrational levels near dissociation and to the continuum in Na2

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Abstract
Unidirectional laser oscillation of Na2 dimers has been observed using 5682-Å single-mode Kr+ laser pumping. This laser action involves not only bound-bound transitions, but also (for the first time) bound-free transitions between two strongly bound electronic states (the A 1Σ+u and X 1Σ+g states). Twelve bound-bound transitions and two regions of bound-free emission, in the region 7200–8300 Å, were observed. Previously reported laser-induced fluorescence results were used to assign both the bound-bound and bound-free transitions to the A 1Σ+u –X 1Σ+g band system of Na2. The bound-bound transitions are also of particular interest because they all occur to very highly excited vibrational levels within 10% of dissociation (laser oscillation to lower levels should also be possible but was not examined). The pressure for optimum intensity was found to be ∼0.65 Torr.