Two -Photon Resonance Fluorescence in a Ladder System

Abstract

In this thesis we consider a three-level ladder-type atom driven by a coherent laser. When driven on two-photon resonance, the atom is excited into its highest state by absorbing two photons simultaneously, followed by a cascaded decay. Employing techniques derived from the Lindblad master equation, we solve for the first-order correlation function, from which we can calculate the fluorescence spectrum. We find that under a strong drive field, the fluorescence spectrum contains up to seven different peaks. We aim to explain the emergence of these peaks by looking at transitions amongst the atom's dressed states. We then aim to characterise the nature of the emitted light by investigating the second-order correlation function. In order to obtain a more precise picture of the photon correlations, we introduce a frequency filtering technique that allows us to isolate individual transitions. Measuring the photon correlations of these transitions provides a more complete picture of the role of specific dressed states of the system. We provide mostly numerical surveys of the fluorescence spectrum and correlations, with some analytic expressions to verify results.