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The Journal of Chemical Physics

Electromagnetically induced transparency in a Λ-type molecular system with permanent dipole moments revisited

Niharika Singh, Q. V. Lawande, Richard D’Souza, B. N. Jagatap

Published Sep 12, 2012• 6 citations
Publisher

Abstract

Electromagnetically induced transparency (EIT) in a molecular three-level Λ system with permanent dipole moments and undergoing m- and n-photon transitions by pump and probe lasers is investigated. Analytical expressions are derived for probe absorption spectrum and dispersion for a medium of stationary as well as thermal molecules. Contrary to the earlier study by Zhou et al. [J. Chem. Phys. 131, 034105 (2009)], we observe no amplification in 2 + 2 photon process when the sign of the difference of the permanent moments of the excited and the ground levels is reversed. Reasons for these contrasting observations are discussed. Our study shows that the permanent moments essentially damp the laser-molecule Rabi frequency to result in narrower EIT line width and larger group velocity index. These effects are further enhanced when the order of the multi-photon process is increased. The importance of the virtual mechanism is discussed by considering the special case of 2 + 1 photon EIT.

DOI
10.1063/1.4751445

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Acta Physica Sinica•Jan 1, 2008•10 citations
Electromagnetically induced transparency (EIT) in a molecular three-level Λ system with permanent dipole moments and undergoing m- and n-photon transitions by pump and probe lasers is investigated. Analytical expressions are derived for probe absorption spectrum and dispersion for a medium of stationary as well as thermal molecules. Contrary to the earlier study by Zhou et al. [J. Chem. Phys. 131, 034105 (2009)], we observe no amplification in 2 + 2 photon process when the sign of the difference of the permanent moments of the excited and the ground levels is reversed. Reasons for these contrasting observations are discussed. Our study shows that the permanent moments essentially damp the laser-molecule Rabi frequency to result in narrower EIT line width and larger group velocity index. These effects are further enhanced when the order of the multi-photon process is increased. The importance of the virtual mechanism is discussed by considering the special case of 2 + 1 photon EIT.
Electromagnetically induced transparency in a three-level Lambda-type molecular system with nonzero permanent dipole moments is investigated. It is shown that in the (2+2)-transition processes, when the sign of d(21), the difference in permanent dipole moments of the probe transition, is positive, perfect electromagnetically induced transparency with steep normal dispersion could be obtained under specific conditions. In contrast, when the sign of d(21) is negative, surprisingly gain without inversion with steep anomalous dispersion could be attained.
Electromagnetically induced transparency (EIT) in a molecular three-level Λ system with permanent dipole moments (PDMs) and the control beam in Laguerre–Gaussian (LG) mode is investigated. The results are compared with the atomic system where the use of LG mode yields EIT linewidth narrower than that with Gaussian mode. It is shown that in contrast to the atomic system, the linewidth of EIT in the dipolar molecular system with LG mode can be narrower as well as broader than that with Gaussian mode depending on the strength of the effective laser-molecule coupling. Peculiar space dependence of Bessel function in the laser-molecule coupling is at the origin of this distinctive feature. The results are further augmented by a discussion on PDM-mediated multi-photon absorption and multi-photon EIT profiles with LG and Gaussian modes.
We have theoretically studied the atomic populations, electromagnetically induced transparency (EIT), and dispersion in a three-level Λ-type system. The density matrix equations are set up with regard for the relaxation of populations of the ground states, and the optical Bloch equations are solved analytically in the weak probe field approximation. Decoherence effects in the ground and excited states on the EIT line shape and dispersive signals are studied, and it is found that the EIT line width increases and the peak height decreases, as the decoherence rates increase in the ground and excited states. On the other hand, we have observed that the dispersive signals are steeper and of high contrast for the lower decoherence rates in the ground and excited states. We have also analyzed the variations of atomic populations of the energy levels at the pump Rabi frequency, as well as the decoherence rate in the ground state.
The transient properties of electromagnetically induced transparency (EIT) with different pump laser energies in a Λ-type three-level system are studied by solving the time-dependent matrix equation. The time evolution of the probe laser absorption, the population of the three levels and the coherent term ρ 23 are analyzed. It is shown that transient amplification without inversion can be realized with high pump laser energy and that transient EIT would reduce and transient amplification without inversion would disappear with the decrease of the pump laser energy. Since the probe absorption depends on the product of Rabi frequency of the pump laser and the coherent term ρ 23, the nonzero damping coherent term ρ 23 results in the transient absorption and amplification without inversion at high pump laser energy, and the decrease of the coherence with the decrease of the pump laser energy leads to the disappearance of the amplification and enhancement of absorption.
Abstract Electromagnetically induced transparency (EIT) plays an essential role in quantum communication and photon storage. Investigating the EIT phenomenon in molecular aggregates is of significant importance for understanding the coherence properties and nonlinear behaviors of the systems. In this paper, we consider molecular aggregates composed of identical molecules, including single and double molecular chains, and investigate their dynamics under the combined excitation of probe and control light fields. Using the truncated sets of differential equations derived from the quantum Master equation, populations of the excited band and their properties are obtained. The results show that EIT occurs when the frequency of the control light field is near-resonant with the transition frequency between the first excited state and a higher excited state of the individual molecules. EIT is more likely to appear under weak coupling conditions, while a stronger field intensity leads to the appearance of the Autler–Townes phenomenon. The clear EIT window can take place for some specific orientations of the molecular dipole moments. A transition between electromagnetically induced absorption and EIT is found in a double chain configuration. Our study provides a platform for understanding the EIT mechanism in molecular systems and offers theoretical guidance for the design of molecular-based quantum devices.
Electromagnetically induced transparency (EIT) resonance is obtained in a well-studied lambda three level system where an optical coupling field and a probing field interact with two optical transitions. However, both electromagnetically induced absorption (EIA) and EIT can be obtained in a modified quasi-lambda four level system consisting of an optical-radio two-photon coupling field and a probing field. By solving the density matrix equation of motion, a physical account of EIA and EIT is given in terms of a dressed state picture. It can be seen that the optical coupling field in this quasi-lambda four level system has a crucial effect on the forming of EIA and EIT. An EIA is observed under a resonant optical coupling and it evolves into an EIT when there is a detuning. Furthermore, the width of EIA or EIT increases as the optical coupling Rabi frequency increases.