Atomic coherences of on-resonant and off-resonant two-photon absorptions in a ladder-type atomic system

Abstract

We report the physical origins of the on-resonant and off-resonant two-photon absorption (TPA) in an open-ladder-type atomic system of the 5S1/2(F=1)-5P3/2(F′=0,1,2)-5D5/2(F′′=1,2,3) transitions in Rb87 atoms. When the on-resonant TPA, including electromagnetically induced transparency (EIT), was transformed into the off-resonant TPA according to the coupling laser frequency detuning, we clarified the dynamics of the atomic coherences by decomposing into the two-photon coherence (TC) and the crossover coherence (CC) terms mixed between one-photon coherence (OC) and TC terms. The physical origins of the two TPAs were completely different; the cause of the on-resonant TPA was the CC term, and that of the off-resonant TPA was the TC term.