We have recorded the 4sns 'So (n = 14-31), 4snd 1D 2 (n = 12-35), 4snf " 3 F' (n -8 to n = 26), and 4snp 3 Po 1 2 (n = 10 to n = 40) Rydberg series of Zn. We applied various excitation schemes that use two and three laser beams interacting with the Zn vapor in a heat-pipe-like oven with subsequent thermionic detection of the excited states. From the quantum defects of the nonpenetrating 4snf levels we estimated the effective dipole polarizability of the Zn+ core to be a = 2.30 -0.12 x 10-24 cm 3 .

We have recorded the - 50) bound Rydberg spectrum of cadmium. We have fully resolved the multiplet up to n = 19 and partially up to n = 24. Furthermore, we have observed the odd singlet and triplet 5sn f Rydberg series for n = 10 - 22 and n = 4 - 21, respectively. We have applied two- and three-step laser schemes to excite Cd vapour in a heat pipe-like oven which was operated as a thermionic diode for detection. Theoretical calculations were performed for the energies of the 5sn p and 5sn f series using perturbation theory with a zero-order model approximation. There is a good agreement between theoretical and experimental results for the 5sn p series, the deviation decreasing with n and being 1 - 2 for n = 50. The agreement for the 5sn f is satisfactory. From the quantum defect of the 5sn f series we approximate a value of the effective dipole polarizability of the ion of in units of the Bohr radius.

We report what is to our knowledge the first observation of phase-conjugate waves by degenerate four-wave mixing in Ba vapor near its 6s(2)(1)S(0) ? 6s6p(1)P(1) resonance transition. A maximum reflectivity of 36% at 10 mbars of Ar buffer gas pressure is observed together with a temporal pulse shortening of 50%. Conical emission in the two pump waves after their passage through the nonlinear medium is also observed. The dependence of the phase-conjugate signal on the pressure of the Ar buffer gas shows a small state-changing collisional decay rate.