Wave mixing and amplified spontaneous emission in pure potassium and mixed sodium-potassium vapors

We report observations of several wave-mixing and stimulated processes in pure potassium and mixed sodium-potassium vapors which are excited by a pulsed laser operating in the range 680–800 nm. When the laser is tuned to the potassium two-photon 4S6S transition, we observe stimulated emission on the various cascade transitions as well as four- and six-wave mixing. When the laser is tuned over the range 747 to 753 nm, which is well away from all atomic transitions, we observe strong forward and weak backward emission at the potassium 3D _3/24P _1/2 transition wavelength (1.17 m). However, this latter emission is only observed in the mixed sodium-potassium vapor. We present data on the excitation spectrum, forward to backward asymmetry, temporal dependence, and the laser power dependence of this emission. We speculate that twophoton photodissociation of the NaK molecule is responsible for this emission.