A theoretical consideration of the effects upon a resonance fluorescence spectrum caused by interference between coupled hyperfine excited states

Abstract

In the context of laser spectroscopy we consider the effects of interference between the spontaneous emission to a common lower level from neighbouring, closely spaced, excited-state levels. In particular the effects on the fluorescence spectrum and on the measured positions of the line centres are described. A formalism, based upon the atomic density matrix, is developed quantitatively to describe these effects within complex hyperfine systems such as the sodium D-lines. Where possible, we have tried to simplify the resultant equations, defining the magnitude of the various fluorescent components and establish a general result for the phase of each component. Finally, the formalism is applied to the particular case of the sodium D1-line, where very different results are obtained depending on whether optical pumping into unobserved states is included, or omitted, from the calculation.