Spectroscopy of Ultra-cold 39K Rydberg Atoms in an AC-driven Magneto-Optical Trap (AC-MOT).

Results from measurement of the energy levels of ultra-cold Rydberg states of 39K in an AC-Magneto-Optical Trap are presented. Rydberg atoms are produced by stepwise excitation from the laser-excited 42P1/2 states using a tunable blue dye laser. Energy level data for principal quantum numbers n = 18 up to n = 199 are reported. For n = 18 to n = 46, the measured levels are in good agreement with the available data from the National Institute of Standards and Technology (NIST) list of atomic spectral lines. New values for the parameters in the Rydberg-Ritz formula were then calculated from a fit to the measured energy level data. Atomic transition energies for n = 47 to n = 199 are also reported for the first time. Shifts in the levels for excitation to both the 2S 1/2 and 2D3/2 states at principal quantum number n &gt; 100 are found when compared to calculations derived from the revised Rydberg-Ritz formula. These deviations are due to the greater probability of overlap between the wavefunctions of the excited atoms in the ensemble, resulting in strong interaction between the Rydberg atoms which are in close proximity. For n &gt; 167, the D-state energies were unresolved.<br/>