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Laser Physics

Theoretical study of coherent optical phenomena in a three lasers driven four-level ladder-type system involving a Rydberg state

Rohit Hazra, Md. Mabud Hossain

Published May 13, 2022• 3 citations
Publisher

Abstract

Abstract A comparative theoretical study of two-photon electromagnetically induced transparency (EIT), absorption (EIA) and three-photon electromagnetically induced transparency (TPEIT), absorption (TPEIA) and their associated dispersion and group index profiles are presented by using a four-level ladder-type system of both stationary and moving 85 Rb Rydberg atoms. We have observed EIT, EIA and their respective positive and negative dispersive slopes under two-photon conditions, while the TPEIT, TPEIA signals and the respective multiple positive and negative dispersive slopes at around zero detuning of the probe field are observed under the three-photon conditions. It is found that the control and manipulation of the coherent optical responses under three-photon conditions are much richer than the two-photon conditions. The group index profiles related to the dispersion of the medium have been studied under both two- and three-photon conditions to compare and explain the optical switching between the subluminal and superluminal modes of propagation for both stationary and moving atomic medium. The influence of the ‘pump’ Rabi frequency on the group index has also been investigated to illustrate the action of optical switching. Finally, the existence of the four-wave mixing (FWM) process due to the action of three optical fields in the EIT medium is also discussed.

DOI
10.1088/1555-6611/ac641d

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Abstract A comparative theoretical study of two-photon electromagnetically induced transparency (EIT), absorption (EIA) and three-photon electromagnetically induced transparency (TPEIT), absorption (TPEIA) and their associated dispersion and group index profiles are presented by using a four-level ladder-type system of both stationary and moving 85 Rb Rydberg atoms. We have observed EIT, EIA and their respective positive and negative dispersive slopes under two-photon conditions, while the TPEIT, TPEIA signals and the respective multiple positive and negative dispersive slopes at around zero detuning of the probe field are observed under the three-photon conditions. It is found that the control and manipulation of the coherent optical responses under three-photon conditions are much richer than the two-photon conditions. The group index profiles related to the dispersion of the medium have been studied under both two- and three-photon conditions to compare and explain the optical switching between the subluminal and superluminal modes of propagation for both stationary and moving atomic medium. The influence of the ‘pump’ Rabi frequency on the group index has also been investigated to illustrate the action of optical switching. Finally, the existence of the four-wave mixing (FWM) process due to the action of three optical fields in the EIT medium is also discussed.
Abstract We report a theoretical investigation of the dispersion resulting from electromagnetically induced transparency (EIT) and the associated group refractive index profiles n g of a four-level inverted Y-type system formed by the interaction of three optical fields (probe, pump and control) with 87Rb atoms. The density matrix equations are derived from the semi-classical Liouville’s equation and solved both numerically and analytically to study the coherent nonlinear optical properties of the medium. We first present the EIT, dispersion and corresponding group index profiles n g under the switch-on/off and on/off-resonance conditions of the pump and control lasers. In presence of both pump and control lasers, an enhancement of the EIT window, a sharp EIT spike and related steeper dispersion slopes are obtained at the line centre of the probe frequency detuning. The group index profiles with the variation of the strengths of individual applied optical fields are studied. The effect of the ground state decoherence rates on the group index profile is examined in detail. It is found that the manipulation of n g values and the corresponding group velocities ν g of the probe light can be easily controlled from subluminal to superluminal values or vice versa by changing the strengths of the applied fields and the ground state decoherence rates. Besides, the EIT-based ‘optical switching’ phenomenon in the medium is explained by studying the variation of the group index with the pump and control Rabi frequencies.
Rb atoms. By comparing the FWM spectra with the electromagnetically induced transparency (EIT) spectra of the hyperfine states, we confirm that the FWM process is significantly influenced by both ladder-type and V-type two-photon coherences. From the observed FWM signal of each hyperfine structure, we clarify the role of two-photon coherence in the FWM process under EIT, double-resonance optical pumping (DROP), and two-photon absorption (TPA) conditions in a ladder-type atomic system, which is dependent on the open degree of the hyperfine states, the laser intensity, and the laser frequency detuning.
Abstract We study various coherent optical properties, e.g., two-photon electromagnetically induced transparency (EIT) and three-photon electromagnetically induced transparency and absorption (TPEIT/TPEIA), in a four-level ladder (Ξ)-type system of 87Rb atoms, where the probe and control fields are Gaussian-shaped laser beams and the pump field is structured laser beam. Additionally, the generated four-wave mixing (FWM) signal has been studied. Interestingly, it is found that the generated FWM signal is spatially structured along with the azimuthal phase, which carries the orbital angular momentum (OAM) of light. It is also observed that the coherent optical responses (EIT, TPEIT/TPEIA, and FWM signals) can be manipulated by utilizing the OAM number of the pump beam as a control knob.
Abstract We theoretically study the two- and three-photon coherence in a Ξ−Λ type four-level system for stationary as well moving atoms at the room temperature using density matrix formalism. We discuss the role of dressed states to elucidate the electromagnetically induced transparency and electromagnetically induced absorption phenomena. The presence of the third field induces absorption at the line centre. A negative dispersion slope owing to the enhanced absorption results in super-luminal light propagation and the group index variation with the coupling field is switched from sub- to super-luminal. Group index with probe detuning shows super-luminal light propagation behaviour at the dressed state positions. The three optical fields trigger four-wave mixing as a result of the third order nonlinearity. The transient evolution is also discussed for optimum strengths of the coupling and drive fields to realize the optical switching in the system.
Using density matrix eqution, the absorption and dispersion properties of a A-type four-level system driven by coherent fields are investigated. The result obtained by means of numerical method indicates that by adjusting the intensity of Rabi frequencies of the coherent field in the steady state, three, double or single electromagnetically induced transparency (EIT) can appear explicitly in this system. And the explanations of these phenomena are given by using the dressed states. In the three EIT, the location of transparent windows can be manipulated by controlling the detuning of the driving field. What's more, it is also found that the medium shows a large refractive index at each transparency window, and the group velocity of the probe laser can be enhanced.
Abstract Electromagnetically induced transparency (EIT) and absorption (EIA) are quantum coherence phenomena which result from the interference of excitation pathways. Combining these with Rydberg atoms have opened up many possibilities for various applications. We introduce a theoretical model to study Rydberg-EIT and Rydberg-EIA effects in cold Cs and Rb atomic ensembles in a four-level ladder type scheme taking into account van der Waals type interactions between the atoms. The proposed many-body method for analysis of such systems involves a self-consistent mean field approach and it produces results which display a very good agreement with recent experiments. Our calculations also successfully demonstrate experimentally observed EIT-EIA cross-over in the Rb case. Being able to simulate the interaction effects in such systems has significant importance, especially for controlling the optical response of these.