Production of very-high-n strontium Rydberg atoms

The production of very-high-n (n similar to 300-500) strontium Rydberg atoms is explored using a crossed-laser-atom-beam geometry. n(1)S(0) and n(1)D(2) states are created by two-photon excitation via the 5s5p P-1(1) intermediate state using radiation with wavelengths of similar to 461 and similar to 413 nm. Rydberg atom densities as high as similar to 3 x 10(5) cm(-3) have been achieved, sufficient that Rydberg-Rydberg interactions can become important. The isotope shifts in the Rydberg series limits are determined by tuning the 461-nm light to preferentially excite the different strontium isotopes. Photoexcitation in the presence of an applied electric field is examined. The initially quadratic Stark shift of the n(1)P(1) and n(1)D(2) states becomes near-linear at higher fields and the possible use of n(1)D(2) states to create strongly polarized, quasi-one-dimensional electronic states in strontium is discussed. The data are analyzed with the aid of a two-active-electron (TAE) approximation. The two-electron Hamiltonian, within which the Sr2+ core is represented by a semi-empirical potential, is numerically diagonalized allowing the calculation of the energies of high-n Rydberg states and their photoexcitation probabilities.