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Journal of Physics Conference Series

Identification of strong one-step two-photon absorption in a cascade three-level system

Ji‐Cai Liu, Lei Chen, Ye-Qi Zhang

Published Apr 10, 2014• 0 citations
Publisher

Abstract

The ultrafast one-step and two-step two-photon absorption processes in a cascade three-level system induced by a strong femtosecond laser pulse is studied. The strong change of the population in the two-photon absorption state at the zero points of the first derivative of the population in the real intermediate state shows straightforwardly in time domain the footprint of the coherent one-step two-photon absorption.

DOI
10.1088/1742-6596/488/3/032052

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The ultrafast one-step and two-step two-photon absorption processes in a cascade three-level system induced by a strong femtosecond laser pulse is studied. The strong change of the population in the two-photon absorption state at the zero points of the first derivative of the population in the real intermediate state shows straightforwardly in time domain the footprint of the coherent one-step two-photon absorption.
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We show that it is possible to use a single sideband to induce two-photon transparency in a three-level cascade medium. The medium simultaneously absorbs two photons as a one-step process when the middle level is far off one-photon resonance. A resonant sideband coupling on the upper transition and the two-photon one-step process drive the medium into a trapped state, and the dominant component is the ground state. Thus almost all population is trapped in the ground state and the two-photon absorption is dramatically suppressed. We present a numerical calculation for arbitrary values of the atomic and field parameters and also provide an analytic description for the required conditions.
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