Term Values, Pressure Broadenings and Shifts in High Rydberg Levels of Rubidium

Abstract

The Doppler-free linewidth and dramatic increase in sensitivity characteristic of two-photon absorption using counter-propagating laser beams, has made this an important technique for studies of highly-excited Rydberg states. In this paper, we present the results of recent investigations of two-photon spectra in atomic rubidium as examples of the type of information obtainable from such spectra. Wavelengths of the transitions n2S←52S (with n=9 to 116), and n2D←52S (with n=7 to 124) have been measured with a precision of 1 part in 107. Series formulae have been computed for the term values, leading to accurate values for the ionization limit and quantum defects. Fine and hyperfine structure splittings have been measured, and the isotope shift for 85Rb and 87Rb evaluated. Measurements of self-broadening and frequency shifts have been made for Rb pressures in the range 1 to 100 mTorr. For both series of lines, frequency shifts are to the red; the rate increases rapidly with n, and remains constant for n>40. For the 2S series, the linewidths exhibit a highly oscillatory behaviour with n, the peaks being approximately equally spaced in n.