We characterize the effect of quantum interference of light scattering on the line shapes and measured line positions in atomic spectra. These effects occur when the excited state splittings are of order the excited state line widths, and represent an overlooked but significant systematic effect. We show that excited state interference gives rise to non-Lorenztian line shapes that depend on excitation polarization, and we present expressions for the corrected line shapes. We analyze the spectra of 6;7Li D lines taken at multiple excitation laser polarizations and show that failure to account for interference changes the inferred line strengths and shifts the line centers by as much as 1 MHz. Using the correct lineshape we present a reappraisal of the 6;7Li 2s-2p isotope shift and relative nuclear charge radius. This analysis should be important for a number of precise spectral measurements that include partially resolved atomic lines.
Physical Review A
absolute transition frequencies, atomic spectroscopy, line shape, lithium, polarization, quantum interference