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The Journal of Physical Chemistry A

Observing Population Transfer in a Two-Photon Dressed Field Three-Level System by Transient Stimulated Emission

Huei Tarng Liou, Kuang Lang Huang, Benjamin Fain

Published Dec 1, 1997• 0 citations
Publisher

Abstract

In a three-level CS 2 system coupled with two pulsed photon fields, we have observed stimulated emission at a time when the stimulating photon pulse precedes the pump photon pulse by 2.5 pulse widths. This counterintuitive time sequence in photon−matter interaction was interpreted by a model as emission resulting from photon dressed transient states (superposition of molecular quantum states in a Schrödinger equation approach) evolution. The model calculation is also able to simulate the observed quantum interference between two populated levels.

DOI
10.1021/jp9710401

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In a three-level CS 2 system coupled with two pulsed photon fields, we have observed stimulated emission at a time when the stimulating photon pulse precedes the pump photon pulse by 2.5 pulse widths. This counterintuitive time sequence in photon−matter interaction was interpreted by a model as emission resulting from photon dressed transient states (superposition of molecular quantum states in a Schrödinger equation approach) evolution. The model calculation is also able to simulate the observed quantum interference between two populated levels.
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We have solved the time-dependent Schr\"odinger equation to analyze the time evolution of a hydrogen atom, initially in its ground 1s state, interacting with a one- or two-color linearly polarized laser pulse which is tuned close to a two-photon resonance with the 2s metastable state. The two-photon transition therefore does not involve an intermediate resonance state. Using a suitable combination of two laser pulses of different frequencies, population can be transferred from the 1s state to the 2s state via the continuum. In both the single-color and the two-color cases, a maximum amount of 17% of population can be found in the 2s state at the end of the pulse. We compare and interpret our results in terms of the time-independent Floquet eigenvalues. The system can also be modeled by an ``essential states'' two-level atom with decay. Both the Floquet and the time-dependent solutions are compared with the model predictions. The model allows systematic optimization studies for population transfer under a wide range of laser pulse parameters.
We report the measurement of the transient intersubband absorption in a coupled quantum well semiconductor structure. Pulsed interband excitation is used to prepare a coherent population in the two lowest states of a three level system of electronic subbands. The time-dependent absorption to the upper state is probed by midinfrared time-domain spectroscopy. For certain pump–probe delay times we observe in the intersubband absorption spectra typical signatures of quantum interference: regions with reduced or enhanced absorption.