Isotope shifts and hyperfine structure in calcium 4snp P-1(1) and 4snf F Rydberg states

Isotope shifts and hyperfine structure have been measured in 4snp, P-1(1) a nd 4snf F Rydberg states for all stable calcium isotopes and the radioisoto pe Ca-41 using high-resolution laser spectroscopy. Triple-resonance excitat ion via 4s(21)S(0) --> 4s4p P-1(1) --> 4s4d D-1(2) --> Rydberg state was fo llowed by photoionization with a CO2 laser and mass selective ion detection . Isotope shifts for the even-mass isotopes have been analyzed to derive sp ecific mass shift and field shift factors. The apparent isotope shifts for Ca-41 and Ca-43 exhibit anomalous values that are n-dependent. This is inte rpreted in terms of hyperfine-induced fine-structure mixing, which becomes very pronounced when singlet-triplet fine-structure splitting is comparable to the hyperfine interaction energy. Measurements of fine-structure splitt ings for the predominant isotope Ca-40 have been used as input parameters f or theoretical calculation of the perturbed hyperfine structure. Results ob tained by diagonalizing the second-order hyperfine interaction matrices agr ee very well with experimentally observed spectra. These measurements allow the evaluation of highly selective and sensitive methods for the detection of the rare Ca-41 isotope.