Measurement of absolute transition dipole moment functions of the 3 ¹Π →1 (X) ¹∑⁺ and 3 ¹Π →2 (A) ¹∑⁺ transitions in NaK using Autler-Townes spectroscopy and calibrated fluorescence

We describe a two-laser experiment using optical-optical double resonance fluorescence and Autler-Townes (AT) splittings to determine the NaK 3 ¹Π →1 (X) ¹∑⁺, 2 (A) ¹∑⁺ absolute transition dipole moment functions. Resolved 3 ¹Π →A ¹∑⁺ and 3 ¹Π →X ¹∑⁺ fluorescence was recorded with the fR_equencies of a titanium-sapphire laser (L1) and a ring dye laser (L2) fixed to excite particular 3 ¹Π (v=19,J=11,f) ←A ¹∑⁺ (v′, J′ =J=11,e) ←X ¹∑⁺ (v″, J″ = J′ ±1,e) double resonance transitions. The coefficients of a trial transition dipole moment function μ_e (R) = a0⁺ a1 (R_eq /R) 2 ⁺ a2 (R_eq /R) 4⁺... were adjusted to match the relative intensities of resolved spectral lines terminating on the lower A ¹∑⁺ (v′,11,e) and X ¹∑ ⁺ (v″,11,e) levels. These data provide a relative measure of the functions μ_e (R) over a broad range of R. Next, L2 was tuned to either the 3 ¹Π (19,11,f) ←A ¹∑⁺ (10,11,e) or 3 ¹Π (19,11,f) ←A ¹∑⁺ (9,11,e) transition and focused to an intensity large enough to split the levels via the AT effect. L1 was scanned over the A ¹∑ ⁺ (10,11,e) ←X ¹∑⁺ (1,10,e) or A ¹∑⁺ (9,11,e) ←X ¹∑⁺ (0,12,e) transition to probe the AT line shape, which was fit using density matrix equations to yield an absolute value for μ_ik = ψ _vib i (R) μ_e (R) ψ _vib (R) dR, where i and k represent the upper and lower levels, respectively, of the coupling laser (L2) transition. Finally, the values of μ_ik were used to place the relative μ_e (R) functions obtained with resolved fluorescence onto an absolute scale. We compare our experimental transition dipole moment functions to the theoretical work of Magnier [J. Mol. Spectrosc. 200, 96 (2000)].