Interference between electromagnetically induced transparency and two-step excitation in three-level ladder systems

Abstract

We have performed electromagnetically induced transparency (EIT) and two-photon absorption experiments in ladder-type three-level systems in a hot sodium atomic vapor, using the 3S1/2-3P1/2-4D3/2, 3S1/2-3P3/2-4D3/2,5/2, 3S1/2-3P1/2-5S1/2, and 3S1/2-3P3/2-5S1/2 transitions. In particular, in the most pronounced 3S1/2-3P1/2-4D3/2 system, we have observed quite unique spectral line shapes that are superpositions of sharp dips and peaks, in contrast to ordinary EIT spectra. The peaks and dips have apparently different physical origins, and the line shape can be interpreted as the interference between EIT and two-step excitation.