Four-level Atomic Medium Research Articles

High refractive index and lasing without inversion in an open four-level atomic system

In this letter, a novel atomic scheme is proposed to study the transient evolution of the atomic response with applications to lasing with and without population inversion. We introduce an open four-level atomic medium and compare its transient properties with the corresponding closed system. The impact of cavity parameters i.e. the atomic exit rate from cavity and atomic injection rates on transient response of weak probe field of open system are investigated. It is realized that existence of cavity parameters leads to some interesting results such as large amplification, high refractive index without absorption as well as lasing with and without inversion. These results cannot be obtained in corresponding closed system, due to lack of atomic exit and injection rates. This extra controllability and flexibility, makes open four-level system much more practical than its counterpart closed one.

All-optical switching in a photonic crystal with a defect containing anN-type four-level atomic system

We study the transmission spectra of a one-dimensional photonic crystal with a defect containing a four-level atomic medium that exhibits a greatly enhanced third-order susceptibility while having a vanishing linear susceptibility dependent on the electromagnetically induced transparency. Two ways of controlling the transmission of a photonic crystal are discussed: via absorption, i.e., nonlinear (two-photon) absorption of the probe field enhanced by constructive quantum interference, and via dispersion, which comes down to shifting the resonance frequency of the defect mode for the probe field by varying the refractive index based on the giant Kerr nonlinearity (cross-phase modulation). We demonstrate that such systems enable nonlinear all-optical switching at ultralow intensities of the coupling and switching laser fields.

Controllable steep dispersion with gain in a four-level N-scheme with four-wave mixing

We present a theoretical analysis of the propagation of light pulses through a medium of four-level atoms, with two strong pump fields and a weak probe field in an N-scheme arrangement. We show that four-wave mixing has a profound effect on the probe-field group velocity and absorption, allowing the probe-field propagation to be tuned from superluminal to slow-light regimes with amplification.

Giant Kerr nonlinearity in a four-level atomic medium

The linear and nonlinear response of a driven four-level Λ-type atomic system with two fold lower-levels with three driving fields is investigated. It is found that the giant Kerr nonlinearity can be achieved just by tuning the intensity of coupling fields. Maximal Kerr nonlinearity with zero linear and nonlinear absorption enters the EIT window. Also it is found that the relative phase between applied fields can change the Kerr nonlinearity behavior.

Controlling the optical bistability and transmission coefficient in a four-level atomic medium

A novel four level atomic configuration is proposed for controlling the optical bistability and transmission coefficient with application on all-optical switching. Two circularly polarized components from a weak linearly-polarized probe beam are interacted separately by two transitions of this medium. A coherent coupling field has derived another atomic transition. It is demonstrated that the transmission coefficient of two orthogonally polarized beams at different frequencies can be achieved by adjusting the magnitude of the external magnetic field. It is found that the threshold of the optical bistability can be controlled by magnitude of the external magnetic field. Also, it is shown that optical bistability can be converted to optical multistability by switching the two orthogonally polarized beams.

Coherent control of the Goos-Hnchen shift in four-level atomic medium

The manipulation of the Goos-Hnchen shifts in the reflected and transmitted light beam through a cavity containing four-level atomic medium is investigated by modifying the dispersion-absorption properties of the intracavity medium. Via two external coherent control fields, the Goos-Hnchen shifts of the reflected and transmitted beam can be easily controlled. It is found that around the transparent region of the medium, the Goos-Hnchen shifts are very sensitive and can be enhanced as compared with strong absorption and amplification.

Proposal for efficient two-dimensional atom localization using probe absorption in a microwave-driven four-level atomic system

The behavior of two-dimensional (2D) atom localization is explored by monitoring the probe absorption in a microwave-driven four-level atomic medium under the action of two orthogonal standing-wave fields. Because of the position-dependent atom-field interaction, the information about the position of the atom can be obtained via the absorption measurement of the weak probe field. It is found that the localization behavior is significantly improved due to the joint quantum interference induced by the standing-wave and microwave-driven fields. Most importantly, the atom can be localized at a particular position and the maximal probability of finding the atom in one period of the standing-wave fields reaches unity by properly adjusting the system parameters. The proposed scheme may provide a promising way to achieve high-precision and high-resolution 2D atom localization.

Negative index of refraction in a four-level system with magnetoelectric cross coupling and local field corrections

This research focuses on a coherently driven four-level atomic medium with the aim of inducing a negative index of refraction while taking into consideration local field corrections as well as magnetoelectric cross coupling, i.e. chirality, within the material's response functions. Two control fields are used to render the medium transparent for a probe field which simultaenously couples to an electric and a magnetic dipole transition, thus allowing one to test the permittivity and permeability of the material at the same time. Numerical simulations show that a negative index of refraction with low absorption can be obtained for a range of probe detunings while depending on number density and the ratio between the intensities of the control fields.

Selective Deflection of Polarized Light Via Coherently Driven Four-Level Atoms in a Double-Λ Configuration

We study the interaction of a weak probe field, having two circular polarized components, i.e., σ− and σ+ polarization, with an optically dense medium of four-level atoms in a double-Λ configuration, which is mediated by the electromagnetically induced transparency with a polarized control light with spatially inhomogeneous profile. We analyse the deflection of the polarized probe light and we find that we can selectively determine which circular component will be deflected after the polarized probe light enters the atom medium via adjusting the polarization and detuning of the control field.

Propagation of twin light pulses under magneto-optical switching operations in a four-level inverted-Y atomic medium

Propagation dynamics of twin laser pulses through a cold four-level inverted-Y atomic medium is investigated theoretically via switching on and off an external magnetic field under the application of a strong driving field. By numerically solving the coupled Bloch–Maxwell equations for atom and field simultaneously on a spacetime grid, our spatio-temporal results clearly show that dynamic control of twin-pulse propagation and magneto-optic dual switching operation are possible in such an inverted-Y system. The proposed scheme may be used for the design of magneto-optic switching and magneto-optic storage devices.

Zero absorption and a large negative refractive index in a left-handed four-level atomic medium

In this paper, we have investigated three external fields interacting with the four-level atomic system described by the density-matrix approach. The atomic system exhibits left-handedness with zero absorption and large negative refractive index. Varying the parameters of the three external fields, the properties of zero absorption and large negative refractive index from the atomic system remain unvarying. Our scheme proposes an approach to obtain a negative refractive medium with zero absorption. The zero absorption property of the atomic system may be used to amplify the evanescent waves that have been lost in the imaging by traditional lenses, and a slab fabricated by the left-handed atomic system may be an ideal candidate for designing perfect lenses.

Left-handedness without absorption in the four-level Y-type atomic medium

In this paper we have investigated three external fields interacting with the four-level Y-type atomic system described by the density-matrix approach. The results show that left-handedness with zero absorption is achieved. The zero absorption property displays the possibility of manipulation by varying the phase and the intensity of the coupling field. Also, the zero absorption property may be used to amplify the evanescent waves that have been lost in imaging by traditional lenses. We propose an approach to obtain a negative refractive medium with zero absorption and the possibility of enhanceingthe imaging resolution in realizing ‘superlenses’.

Electromagnetic chirality-induced negative refraction via atomic coherence

Electromagnetic chirality-induced negative refraction in a four-level atomic medium is investigated by initially preparing coherent states of the atom. We show that the negative refraction can be carried out with deeply depressing absorption and without simultaneously requiring both negative electric permittivity and magnetic permeability in an ideal situation where the two chirality coefficients have the same amplitude but the opposite phase.

Tunable ultranarrow linewidth of a cavity induced by interacting dark resonances

A scheme for obtaining a tunable ultranarrow linewidth of a cavity due to an embedded four-level atomic medium with double-dark resonances is proposed. It is shown that the steep dispersion induced by double-dark resonances in the transparency window leads to the ultranarrow transmission peak. Compared with the case of a single-dark resonance system, the linewidth can be narrowed even by one order under proper conditions. Furthermore, the position of the ultranarrow peak can be engineered by varying the detuning of the control field.

Dynamic control of light propagation and optical switching through an RF-driven cascade-type atomic medium

We study nonlinear optical behaviors in pulse propagation through a medium consisting of four-level cascade-type cold atoms, where a radio-frequency (RF) field couples upper two-folded levels and double-dark resonances (DDRs) can arise. By numerically solving the coupled Bloch–Maxwell equations for atom and field simultaneously in space and time, we demonstrate dynamic control of light propagation and optical switching in such a four-level atomic medium. The proposed scheme may have potential applications in the design of optical switching and optical storage devices.

Ultraslow temporal vector optical solitons in a cold four-level tripod atomic system

We show the possibility of generating ultraslow temporal vector optical solitons in a cold lifetime-broadened four-level tripod atomic medium under Raman excitation. We demonstrate that the two orthogonally polarized components of the low-intensity signal field can evolve into various distortion-free temporal vector optical solitons, such as bright-bright vector solitons with ultraslow group velocity. These results are produced from the balance of self- and cross-phase modulation effects and dispersion. We also show that Manakov temporal vector solitons may be realized by adjusting the corresponding self- and cross-phase modulation and dispersion effects of our system.

Optical bistability and multistability in ladder-type four-level atomic coherence medium

Optical bistability（OB） and optical multistability（OM） behaviour of ladder-type four-level atom in a unidirectional ring cavity driven by three laser fields is studied. Three paths of photon transition are coupled with the laser fields. In this case, the laser field ΩB coupling with two middle levels is very important. When the ΩB is increased, optical bistability threshold significantly decreases and optical multistability appears. The effects of the laser field coupling with two upper levels on optical bistability are also discussed. Furthermore, we analyze the effects of the detuning of probe field and atomic cooperation parameter on OB and OM.

Exhibition of subluminal solitons in a four-level atomic system with two-folded levels

With one weak probe, one strong pumping and one control field, the group velocity dispersion can be balanced by the Kerr effects in a lifetime-broadened four-level atomic medium with two folded levels with proper parameters. This results from the subluminal optical solitons that are formed. Additionally, the conditions for which subluminal solitons occur are given.

Electromagnetically induced transparency in the medium of four-level atoms with upper level doublet

Light absorption and slowing down when traveling in a medium of four-level atoms with a doublet of close-lying upper levels is studied in conditions of electromagnetically induced transparency (EIT). It is shown that the presence of the second upper level leads to an increase in the absorption of the probe pulse. However, a control-pulse-detuning range exists between the doublet levels where light decelerates considerably more than in the case of ideal EIT.

Optical bistability via quantum interference in a four-level atomic medium

We theoretically investigate optical bistability (OB) behaviour in a four-level atomic system confined in a unidirectional ring cavity. It is shown that OB can be controlled by adjusting the intensity of the coupling field and the value of the cooperativity parameter. More importantly, our numerical results show that the threshold intensity of OB can be reduced without decreasing the range of the hysteresis loop via adjusting the effect of spontaneously generated coherence (SGC) or the relative phase between two applied fields. The influence of the frequency detuning of the coupling field on the OB behaviour is also discussed.