Three-level Atomic Medium Research Articles

Pulse propagation in a medium ofΛ-type atoms

The propagation of a weak-field pulse through a medium of three-level atoms is considered. Each atom has a $\ensuremath{\Lambda}$-type level scheme in which the two lower levels are stable. A strong control field drives one of the electronic transitions while the signal field drives the coupled transition under conditions where EIT (electromagnetically induced transparency) is usually operative. The input pulse is slowed and compressed as it enters the medium, adiabatically following the EIT solution. However, if the control field is changed suddenly when the pulse is in the medium, the signal field is transformed into two pulses, one of which propagates as a normal EIT pulse and the other with a different speed and an amplitude that oscillates in time. The temporal oscillations are transformed into both spatial and temporal oscillations as the pulse exits the medium. An analytic expression is derived for the pulse intensity which provides a good approximation to the exact result at all times. It is shown that the oscillating component of the exiting pulse can be spatially compressed in comparison with the input pulse.

Formation and optical control of dissipative vortex solitons in hollow-core optical fibres filled with a cold atomic gas

We consider the problem of formation of optical vortex solitons in a medium of three-level atoms, taking into account the local field effects. The principal possibility of formation of optical solitons controlled by an optical pump wave under the off-resonance Raman conditions of the lambda-type interaction scheme is predicted in an optically dense medium, i.e., in a hollow-core photonic-crystal optical fibre filled with a gas of cold atoms 87Rb.

Dissipative optical solitons in dense media with optical pumping

The problem of nonlinear scattering of optical pulses in a dense three-level atomic medium with continuous pumping is considered with allowance for the local field effects. The physical requirements on the parameters of the medium and field are formulated, and the ranges of these parameters for which stationary solitons are effectively formed in the model of a quartz waveguide doped with 87Rb atoms are determined using variational methods. It is found that disregarding the local field in this model results in violation of soliton stability in the predicted parameter range.

Study of radiofrequency radiation by means of optical effect of electromagnetically induced transparency

We propose a method of all-optical investigation of radiofrequency (RF) radiation based on the coherent effect of electromagnetically induced transparency (EIT). It is shown that if the atomic coherence is perturbed by an RF field, the shape of probe pulse propagating in a three-level Λ-type atomic medium under EIT conditions is modified correspondingly to the temporal structure of the RF pulse. The effect is sensitive to the parameters of the pulse which enables measuring the intensity and the spectrum of the RF pulse. The method can be used for storage and lossless transfer of RF information over long distances using optical pulses.

Generation of Raman polaritons in three-level atomic media

A theory of formation of Stokes field (Raman) polaritons, which arise due to the coherent stimulated Raman scattering of light in an ensemble of three-level atoms placed in a Fabry-Perot cavity in the case of a strong coupling regime, is developed. The dispersion and absorption properties of Raman polaritons are investigated and the conditions for polariton amplification are found. It is shown that for certain pump power values, nonclassical correlations (entanglement) between light and dark polaritons are observed in the system.

Beam Splitting in Induced Inhomogeneous Media

We study the spatial behavior of a deflected beam in a coherent Λ-type three-level atomic medium with an inhomogeneous control laser. When the Rabi coupling by the control laser is in a Gaussian profile, the spatial-dependent refraction index of the atomic medium will result in a beam splitting as well as the deflection of the slow probe light under electromagnetically induced transparency. In terms of the phase difference between the two splitting beams and the position of the splitting, the possible interpretation of the splitting is given in theory.

Transient response in a three-level system with the squeezed vacuum

In this paper, the effects of the squeezed vacuum (SV) on the transient response in a ∨-type three-level atomic medium are investigated. We find that the properties of transient process can be greatly affected by the SV whether the vacuum-induced coherence (VIC) exists or not. The combined influence of the SV and the VIC can dramatically modify the transient absorption and gain. Especially, the transient gain can be almost eliminated in the absence of VIC. And the response time from the transient to the steady situation is dependent on the SV. When including the VIC, the transient and steady optical properties display a reverse variation with the SV. Besides, it is shown that the considerable steady state population without inversion can be always induced by the SV.

Gain-assisted control of the Goos-Hänchen shift

A gain-assisted model is considered to study the Goos-H$\stackrel{\ifmmode \ddot{}\else \"{}\fi{}}{\text{a}}$nchen (GH) shift behavior in the reflected and transmitted light. In this model, a probe light is incident on a cavity containing three-level dilute gaseous atomic medium. The atom-field interaction follows two-photon Raman transitions, and the dielectric susceptibility of the medium exhibits dispersion and gain properties [L. J. Wang, A. Kuzmich, and A. Dogariu, Nature (London) 406, 227 (2000)]. Under appropriate conditions, two gain peaks are observed with anomalous dispersion between the peaks, whereas normal dispersion can be observed at and around the gain maxima. The manipulation of the detuning associated with the probe light field which interacts with the intracavity medium during its propagation through the cavity can lead to a control over negative and positive GH shift in the reflected and transmitted light beam via the anomalous and normal dispersion of the medium.

Spatial solitons in a three-level atomic medium supported by a Laguerre-Gaussian control beam

We investigate the existence and stability of various types of spatial solitons in a three-level atomic medium with Laguerre-Gaussian control beam. Radial and azimuthal modulations of the medium properties, introduced by the control beam, provide possibilities for existence of diverse soliton patterns and dynamics. Beam diffraction provides additional soliton controllability. All types of solitons can be generated at very low input energy at a few-photon level.

Effects of squeezed vacuum on transient optical response in a ∧ system

The effects of the squeezed vacuum (SV) on the transient optical properties in a ∧-type three-level atomic medium with or without the vacuum-induced coherence (VIC) are investigated in this paper. We find that the oscillatory amplitude of the optical spectra, the transient absorption (gain), and the response time from the transient to the steady situation are remarkably dependent on the SV. When including the VIC, the transient and steady optical properties display a reverse variation with the SV. Additionally, it is interesting to find that the steady population distribution is kept at the same value for different initial conditions in the presence of SV.

Relative carrier—envelope phase dependence of resonant propagation of two-colour femtosecond pulses in V-type atomic medium

Using numerical solution of the full Maxwell–Bloch equations, which is obtained by the finite-difference time-domain method and the iterative predictor–corrector method, we investigate the modulation effect of relative carrier–envelope phase (hereinafter referred to as the relative phase) on resonant propagation of two-colour femtosecond ultrashort laser pulses in a V-type three-level atomic medium. It is found that the pulse splitting occurs for a smaller value of relative phase; when the value of relative phase increases to a certain value, only the variation of pulse shape is present and the pulse splitting does not occur any more; moreover, when the value of relative phase is smaller, the pulse group velocity is larger. The relative phase also has an obvious effect on population and spectral property. Different population transfers can be realized by adjusting the value of relative phase. Generally speaking, for the pulses with smaller areas their spectral strengths and frequency ranges decrease obviously with the value of relative phase increasing; for the pulses with larger areas, with value of the relative phase increasing, their spectral strengths decrease remarkably but the relative strengths of the higher frequency components increase significantly, while the spectral frequency range is not varied evidently.

All-optical steering of light via spatial Bloch oscillations in a gas of three-level atoms

A standing-wave control field applied to a three-level atomic medium in a planar hollow-core photonic crystal waveguide creates periodic variations of linear and nonlinear refractive indexes of the medium. This property can be used for efficient steering of light. In this work we study, both analytically and numerically, the dynamics of probe optical beams in such structures. By properly designing the spatial dependence of the nonlinearity it is possible to induce long-living Bloch oscillations of spatial gap solitons, thus providing desirable change in direction of the beam propagation without inducing appreciable diffraction. Due to the significant enhancement of the nonlinearity, such self-focusing of the probe beam can be reached at extremely weak light intensities.

Photon hole nondemolition measurement scheme by electromagnetically induced transparency

We propose a scheme for quantum nondemolition measurement of photon holes based on electromagnetically induced transparency, which allows direct nondestructive detection of the photon holes. We analyze a scheme based on interaction of a photon hole signal and a coherent probe field with a three-level atomic medium. Using recent advances in electromagnetically induced transparency technology, we show that the measurement is nondestructive for very weak photon hole signals.

Effect of detuning on the few-cycle laser pulse propagation in the three-level atomic medium

The effect of detuning on the few-cycle laser pulse propagation in the ladder-type three-level atomic medium is investigated by using the numerical solution from the Maxwell-Bloch equations without the slowly varying envelope and rotating-wave approximations. The results show that in the resonance case, the obvious variation of the pulse form, including the carrierenvelope phase, the pulse duration, the oscillation amplitude and frequency, even the pulse splitting will occur in the propagation, and the output pulse is much different from the input. In the off-resonance case, the varying detuning also can lead to the considerable variation of the pulse form in the propagation. However, with an appropriate detuning, the selfinduced transparency can be realized, and the output pulse exactly the same as the input can be obtained.

Propagation of femtosecond chirped Gaussian pulse in dense three-level Λ-type atomic medium

We investigate propagation of femtosecond chirped Gaussian laser pulse in a dense three-level Λ-type atomic medium by using the numerical solution of the full Maxwell-Bloch equations without the slowly varying envelope and the rotating-wave approximations, and the solution is obtained by PC-FDTD method. It is shown that, variation of the sign and size of the chirp coefficient has considerable effect on pulse propagation property, and the effect is closely relative to size of the pulse area. When the area of chirped pulse is smaller than 4π, splitting doesn’t occur and the chirped pulse evolves gradually to an approximate normal Gaussian pulse (C=0), and this characteristic doesn’t vary with the chirp coefficient varying. However, variation of the chirp coefficient will changed the amplitude and group velocity of the pulse. For the positive chirp(C>0), amplitude and group velocity of the pulse decrease with chirp coefficient increasing, for the negative chirp(CC increasing. Both the chirped pulses with area equal to larger than 4π will split into sub-pulses of different numbers and shapes, the time and number of the pulse splitting will be determined by the sign and size of the chirp coefficient. But in the two cases, the pulse splitting patterns are much different, and the effects of the coefficient are also different. When the pulse area equals 4π, larger chirp coefficient will lead to increased sub-pulse number, but when the pulse area is larger than 4π, larger chirp coefficient will lead to decreased sub-pulse number. In addition, regardless of pulse area being larger or smaller, changing sign and size of the chirp coefficient always produces obvious effect on the atomic population.

周期量级激光脉冲在不同密度的原子介质中传播行为的比较

Using the numerical solution of the full Maxwell-Bloch equations without the slowly varying envelope approximation and the rotating-wave approximation, propagation behavior of few-cycle laser pulse in a dense ladder-type three-level atomic medium is investigated and it is compared with the case in the corresponding dilute medium. It is found that, in the propagation process, time evolution of the pulse in the dense medium is obviously different from that in the dilute medium, and the difference will become more evident with increasing of the initial pulse area. When the initial pulse area is smaller, in the propagating process, the pulse shape in the dilute medium just have a small change; the pulse shape in the dense medium has considerable variation but the pulse splitting doesn't occur. When the initial pulse area is larger enough, for the dense medium case, the pulse splits into sub-pulses with different numbers and shapes at different propagation distances; while for the dilute medium case, variation of the pulse shape is still smaller in propagation process. The cause producing above difference is from two effects in the dense medium: the effect of the local-field correction (LFC) from the near dipole-dipole interaction and effect of stronger polarization field than that in the dilute medium. In which the effect of stronger polarization field plays a main role, but the role of LFC also cannot be neglected,and the stronger polarization field is due to the atomic density increasing .

Propagation of small fluctuations in electromagnetically induced transparency: Influence of Doppler width

The propagation of a pair of quantized fields inside a medium of three-level atoms in $\Lambda$ configuration is analyzed. We calculate the stationary quadrature noise spectrum of the field after propagating through the medium in the case where the field has a general (but small) noise spectrum and the atoms are in a coherent population trapping state and show electromagnetically induced transparency (EIT). Although the mean values of the field remain unaltered as the field propagates, there is an oscillatory interchange of noise properties between the probe and pump fields. Also, as the field propagates, there is an oscillatory creation and annihilation of correlations between the probe and pump quadratures. We further study the field propagation of squeezed states when there is two-photon resonance, but the field has a detuning $\delta$ from atomic resonance. We show that the field propagation is very sensitive to $\delta$. The propagation in this case can be explained as a combination of a frequency dependent rotation of maximum squeezed quadrature with an interchange of noise properties between pump and probe fields. It is also shown that the effect of the Doppler width in a squeezed state propagation is considerable.

Quantum-information storage: A Schrödinger-picture approach

A theory is developed to obtain the state vector for an atom-field system in which a single-photon pulse propagates in an optically dense ensemble of two-level or three-level atoms. The manner in which the field and the atoms become entangled is described, as is the entanglement of the atoms produced by the radiation pulse. Two protocols for quantum-information storage are studied. In the first protocol, the single-photon pulse is totally absorbed in an ensemble of two-level atoms that are embedded in a dielectric host. To arrive at analytical expressions for the state vector, fluctuations of atomic position are neglected and it is assumed that the atoms' transition frequencies are inhomogeneously broadened with a width that is much larger than the bandwidth of the single-photon pulse. In the second protocol, a single-photon pulse is sent into a semi-infinite medium of three-level atoms under the conditions where electromagnetic-induced transparency can occur. It is shown that the usual results of pulse compression and reduced group velocity are recovered. Moreover, an explicit expression for the state vector of the atom-field system is obtained.

Spatial solitons and instabilities of light beams in a three-level atomic medium with a standing-wave control field

Spatial solitons and instabilities of light beams in a three-level atomic medium with a standing-wave control field

Multiplicative noise-induced probability distributions in three-level atomic optical bistability

Effects of multiplicative noise on optical bistability in a three-level atomic medium in a ring cavity are investigated experimentally and theoretically. Steady-state intensity distributions as well as switching and dwell times have been measured as functions of noise strength. System response to an external periodic signal is also explored. It is found that the probability for the system to stay in the upper state increases with increasing noise strength. When a small periodic signal is added to the input field, the probability for the upper state has a maximum as a function of multiplicative noise strength. A simple theoretical model based on nonlinear atomic susceptibility is presented to interpret the experimental observations.