NARROW ABSORPTION-LINES INDUCED BY ELECTRON SHELVING

We investigate the absorption spectrum of a laser-driven V system in w hich one of the upper levels is metastable. If the Rabi frequency of t he laser driving the metastable transition is sufficiently small we fi nd an extremely narrow peak in the stationary absorption spectrum of a weak probe on the strong transition. We give analytical expressions a pproximating the stationary absorption spectrum. The absorption spectr um of a two-level system is investigated for the case where an upper l imit for the time separation of successive emissions is given. The abs orption spectrum then exhibits a delta-function-like peak and using th is we then show that the origin of the narrow peak in the absorption s pectrum can be traced back to electron shelving, i.e. to the existence of light and dark periods in the resonance fluorescence emitted on th e strong transition.