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

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.