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Notes: Abstract We demonstrate that the intriguing 830 nm coherent emission, which is observed when sodium vapor is pumped with a high-power pulsed laser tuned near the 3S→4D two-photon transition, is due to an axially phase-matched six-wave mixing process. This conclusion is based upon the observation of emission near 584 nm, which is coupled to the 830 nm emission in the six-wave mixing process: ω1+ω2=2ωL−ω4D→4P −ω4P→3D . In addition, we have observed coherent emission near 1.16 μm, which is due to an analogous process involving cascade through the 4S (as opposed to the 3D) state. We calculate the wavelengths of all photons involved in these processes using the standard formulas of parametric wave-mixing theory, and show that they can be predicted to within experimental uncertainties. Finally we report observations of significant blue shifts of the 830 nm and 1.16 μm emissions in a mixed sodium-potassium vapor. These shifts can be readily understood by considering the effect of the potassium on the frequency-dependent refractive index of the vapor. Due to these results, other recent interpretations of the 830 nm emission as stimulated excimer emission on the Na2 13Σ g + →13Σ u + band must now be rejected.

Notes: We report the observation of bound–free emission corresponding to the lowest triplet transition 1 3Π→1 3Σ+ of the NaK molecule. In the experiment, specific levels of the upper triplet state were populated directly from the ground state by virtue of spin–orbit induced perturbations between the 1 3Π0 and 2 1Σ+ states. Oscillations in the fluorescence spectra between 1.1 and 1.6 μm reflect the probability distribution (wave function squared) in the bound upper state. We have also carried out quantum mechanical simulations of the fluorescence spectra, based on recent ab initio calculations of the relevant potential curves. These simulations verify the identification of this near-infrared emission and provide a critical test for the calculated potentials.

Notes: In this paper we present near-infrared absorption, thermal emission, and laser-induced fluorescence spectra obtained in high density sodium–potassium mixtures. These spectra are compared to spectra calculated from recently published NaK potentials and dipole moments and the agreement is seen to be quite good. We have also observed significant laser-induced fluorescence to the red of the 2 1∑+ → 1 1∑+ NaK band (A band). From laser power and density dependences of this long-wavelength fluorescence, as well as from comparison to calculated spectra, we have tentatively identified this emission as the lowest NaK triplet band 1 3∏ → 1 3∑+ which has not previously been reported. We have also observed a shoulder or satellite feature in potassium vapor under similar conditions. It is possible that this is a potassium trimer emission band.

Notes: The NaK 1 3Δ state has been studied by the perturbation-facilitated optical–optical double resonance technique. Mixed singlet–triplet levels, A(2)1Σ+(vA,J)∼b(1)3Π(vb,J), were pumped from thermally populated rovibrational levels of the ground state, X(1)1Σ+(vX,J±1), using a single-mode cw dye laser. A single-mode cw Ti:Sapphire laser was then used to further excite the NaK molecules to various 1 3Δ(vΔ,NΔ,JΔ) rovibrational levels which were detected by observing collision-induced 3Λ→a(1)3Σ+ fluorescence in the green part of the spectrum. The measured energies of the 1 3Δ(vΔ,NΔ) levels were fit to a Dunham expansion, and the Dunham coefficients were used to construct the RKR potential curve. Absolute numbering of the 1 3Δ state vibrational levels was established by a comparison of experimental and calculated 1 3Δ(vΔ,NΔ,JΔ)←b(1)3Π(vb,Jb) absorption line strengths. A deperturbation program was used to determine the vibration-dependent 1 3Δ state spin–orbit interaction parameter. Hyperfine structure of the 1 3Δ state was studied, and the Fermi-contact interaction term for this state was determined to be ∼0.0111 cm−1. © 2000 American Institute of Physics.

Notes: Predissociation of a high-lying 1Σ+ state of NaK is studied using the optical–optical double resonance technique. A single-mode ring dye laser is set to a particular 2(A)1Σ+(v,J)←1(X)1Σ+(v′′,J′′) transition. Another single-mode laser (Ti–sapphire) is then used to excite the molecule from the 2(A)1Σ+(v,J) level, to rovibrational levels of a higher predissociating electronic state, which we identify as 6 1Σ+. The predissociation is monitored by the atomic potassium emission on the 3 2D3/2→4 2P1/2 transition at 1.17 μm, while bound state radiative processes are monitored by total violet fluorescence from the upper state to the various rovibrational levels of the ground 1(X)1Σ+ state. By scanning the Ti–sapphire laser, different rovibrational levels of the 6 1Σ+ state can be excited. The vibrational levels probed range from v=13 to 20 with rotational states ranging from 9 to 99. The bound state energy level positions are measured from the center frequencies of lines recorded with the Ti–sapphire laser excitation scans. The 6 1Σ+ state is then described by the following molecular constants which are calculated from the experimental values of the level energies: Te=25 560.373 cm−1, ωe=89.179 26 cm−1, ωexe=0.730 691 cm−1, Be=0.067 327 0 cm−1, αe=0.000 675 35 cm−1, De=−3.298 31×10−8 cm−1, βel=1.518 17×10−8 cm−1. The potential well depth is De=4416.0 cm−1, if we assume the most likely asymptotic limit of Na(3 2S1/2)+K(5 2P1/2). The equilibrium separation is Re=4.158 Å. We also report measured and calculated intensities (Franck–Condon factors) for the 6 1Σ+→1(X)1Σ+ violet band. The absolute predissociation rates of 6 1Σ+ levels are directly measured from the linewidths recorded on the Ti–sapphire laser excitation scans. We measure predissociation rates ranging up to 9.4×109 s−1. The dependence of the absolute predissociation rates on rovibrational quantum numbers is studied with an attempt to predict the shape of the repulsive potential curve causing the predissociation, its crossing point with the bound state, and the type of perturbative interaction leading to the predissociation. The state causing the predissociation is determined from correlation diagrams to be the continuum of either the 3 3Π, the 3 1Π, or the 5 3Σ+ state with Na(3S)+K(3D) dissociation limit. We measure the collisional broadening rate coefficients of some 6 1Σ+←2(A)1Σ+ lines due to both argon and potassium perturbers, and obtain the average values, kbrAr=(1.1±0.2)×10−8 cm3 s−1 and kbrK=(1.1±0.6)×10−8 cm3 s −1. Velocity-changing collisions and collisional excitation transfer between individual rotational levels of the 2(A)1Σ+ state are also investigated. © 1997 American Institute of Physics.

Notes: Abstract Optically pumped laser emission has been observed on the NaK 2(A)1Σ+ → 1(X)1Σ+ electronic state transition. The emission occurs between 1.015 and 1.035 μm when a sodium-potassium heat-pipe oven is pumped with 695–745 nm pulsed dye laser radiation. The laser emission occurs on many ro-vibrational transitions without the use of cavity mirrors. However, the addition of a simple cavity increases both the number of observed lasing transitions and the amplitude of the emission on each line. We report our results for the dependence of the emission intensity on pump laser power, oven temperature, and buffer gas pressure.

Notes: Abstract 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 4S→6S 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 3/2→4P 1/2 transition wavelength (1.17 μm). 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.