Measurement of hyperfine coupling constants in the 3 d 2 Dj levels of 39 K , 40 K , and 41 K by polarization quantum - beat spectroscopy

Hyperfine quantum-beat spectroscopy has been utilized in a pump-probe configuration to measure magnetic dipole (A) and electric quadrupole (B) coupling constants in the 3d D3/2 and 3d D5/2 levels of three isotopes of potassium. For many of these levels, the largest hyperfine splitting is smaller than the natural width, and so a subnatural linewidth technique is required. In the experiments, the 3d levels are excited on the 4d S1/2→3d Dj quadrupole transition with linearly polarized light. Time evolution of the alignment components in the d levels is probed by time-delayed resonant radiation on the 3d Dj→9p P j transitions. Comparison of the excitation rate for two orthogonal relative polarization directions of the pump and probe laser at each delay time permits derivation of a linear polarization degree. This quantity contains beats at the various hyperfine frequencies in the d levels. Fitting the experimentally obtained time dependence to theoretical expressions allows extraction of the hyperfine coupling constants. For the 3d D3/2 level of K we obtain A50.96(4) MHz and B50.37(8) MHz, indicating a typical precision also obtained for the other levels and isotopes. @S1050-2947~97!04905-6#