Time evolution of few-cycle pulse in a dense V-type three-level medium

Propagation of a few-cycle laser pulse in a dense V-type three-level atomic medium is investigated by the numerical solution of the full Maxwell–Bloch equations without the rotating wave and slowly varying envelope approximations, and the numerical solution is obtained by using the predictor–corrector method and the finite-difference time-domain method. It is shown that, due to the strength of the electric field induced by the macroscopic polarization in a dense medium being stronger than that in a dilute medium and the influence of the near dipole–dipole (NDD) interaction, the time evolution of a few-cycle pulse in the dense medium is remarkably different from that in the corresponding dilute medium. In the dilute medium, oscillation arises at the trailing edge of the pulse; while in the dense medium, it appears at both the leading and trailing edges of the pulse; moreover, the oscillation at the leading edge is more obvious with the pulse area decreasing. The carrier-envelope phase has an obvious difference in the two cases with and without NDD interaction. The ratio, γ, of the transition dipole moments has strong influence on the time evolution and split of the pulse. In the dense medium, when?γ?= 1, NDD interaction delays propagation and split of the pulse; while when?γ?> 1, NDD interaction accelerates propagation and split of the pulse, moreover, the phenomenon is more obvious with the input pulse area decreasing. In the dilute medium, the larger area pulse doesn't split when?γ?= 1 while it splits when?γ?> 1.     

Optical force and friction of a V-type three-level atom in a driven high-Q cavity

A model is presented to calculate the optical force and friction for a three-level atom in a V-type configuration in a weakly driven high-finesse cavity. Analytical expressions for the force and friction are derived using Heisenberg equations. It is demonstrated that the cooling rate can be increased by one order of magnitude over that of a two-level atomic system, which would stimulate further experimental investigations.     

Probe polarization on absorption in a V-type medium with vacuum-induced interference

The absorption of a weak probe beam for a V-type atom with a closely spaced doublet is studied under conditions such that vacuum-induced interference among decay channels is important. It is shown how the probe polarization as well as the vacuum-induced interference influence the absorption amplitude and spectral structure. Comparing with similar models studied earlier, where probe polarization direction has not been taken into account, the present study shows that probe polarization has significant effects on the absorption spectra.     

Two different regimes in a V-type three-level atom trapped in an optical cavity

In this paper two different behaviors of a V-type three-level atom which is driven by a classical field in an optical cavity are shown. We show that the behavior of an atom depends on the values of the critical photon number. The system treatment for large enough values of the critical photon number is described by the semiclassical laser theory. In contrast, for small enough values of the critical photon number, the system shows new quantum properties. In the former case, it is shown that the system performs like a conventional laser and in the latter one, the system acts as an effective two-level model. The behaviors of the system are investigated both in the semiclassical approximation and full quantum theory. For comparing the results, computer simulations are implemented.     

Phase effects on group velocity propagation in a V-type system with spontaneously generated coherence

The effects of the relative phase between two laser beams on the propagation of a weak electromagnetic pulse are investigated in a V-type system with spontaneously generated coherence (SGC). Due to the relative phase, the subluminal and superluminal group velocity can be unified. Meanwhile, SGC can be regarded as a knob to manipulate light propagation between subluminal and superluminal.     

Effect of quantum interference on a three-level atom driven by two laser fields

Abstract

We study the effect of quantum interference on the population distribution and absorptive properties of a V-type three-level atom driven by two lasers of unequal intensities and different angular frequencies. Three coupling configurations of the lasers to the atom are analysed: (a) both lasers coupled to the same atomic transition, (b) each laser coupled to different atomic transition and (c) each laser coupled to both atomic transitions. Dressed states for the three coupling configurations are identified, and the population distribution and absorptive properties of the weaker field are interpreted in terms of transition dipole moments and transition frequencies among these dressed states. In particular, we find that in the first two cases there is no population inversion between the bare atomic states, but the population can be trapped in a superposition of the dressed states induced by quantum interference and the stronger field. We show, that the trapping of the population, which results from the cancellation of transition dipole moments, does not prevent the weaker field to be coupled to the cancelled (dark) transitions. As a result, the weaker field can be strongly amplified on transparent transitions. In the case of each laser coupled to both atomic transitions the population can be trapped in a linear superposition of the excited bare atomic states leaving the ground state unpopulated in the steady state. Moreover, we find that the absorption rate of the weaker field depends on the detuning of the strong field from the atomic resonances and the splitting between the atomic excited states. When the strong field is resonant to one of the atomic transitions a quasi-trapping effect appears in one of the dressed states. In the quasi-trapping situation all the transition dipole moments are different from zero, which allows the weaker field to be amplified on the inverted transitions. When the strong field is tuned halfway between the atomic excited states, the population is completely trapped in one of the dressed states and no amplification is found for the weaker field.     

Efficient and monolithic polarization conversion system based on a polarization grating

We introduce a new polarization conversion system (PCS) based on a liquid-crystal polarization grating (PG) and louvered wave plate. A simple arrangement of these elements laminated between two microlens arrays results in a compact and monolithic element, with the ability to nearly completely convert unpolarized input into linearly polarized output across most of the visible bandwidth. In our first prototypes, this PG-PCS approach manifests nearly 90% conversion efficiency of unpolarized to polarized for ±11° input light divergence, leading to an energy efficient picoprojector that presents high efficacy (12 lm/W) with good color uniformity.     

Vector diffraction and polarization effects in an optical disk system

The track pitch of current optical disks is comparable with the wavelength of the laser source. In this domain of the pitch-to-wavelength ratio, the complex-diffraction amplitudes are different for different incident polarization states, and the validity of the scalar diffraction theory is questionable. Furthermore, the use of multilayer coatings and high-numerical-aperture beams in modern optical disk technology inevitably entails the excitation of surface waves, which can disturb the baseball pattern significantly. To describe the interaction of a focused beam with a grooved multilayer system fully, it is necessary to have a rigorous vector theory. We use a rigorous vector theory to model the diffraction of light at the optical disk. We present the simulation and the experimental results and demonstrate the ability of this approach to predict or model accurately all essential features of beam-disk interaction, including the polarization effects and the excitation of surface waves.     

General formalism of interaction of a three-level atom with cavity fields in the Kerr-like medium

Abstract

A general formalism of a three-level atom interacting with one-mode or two-mode cavity fields in a Kerr-like medium is presented. Dynamic behaviours of the atomic occupation probabilities and the transfer phenomena are investigated numerically in two typical cases. Our results show that the transfer phenomena may depend on the initial conditions.     

Berry phase and interference effects in three-level atoms

A theoretical analysis of Berry's phases, which is based on the Cartan subalgebra, is given for three-level atomic systems. The analysis is developed under the adiabatic approximation and is related to topological fibre bundle theories. The topological Berry's phases derived in the present study, are related to phase shifts and can be applied, also, for partial cycles. Some possible applications of the present theory are discussed, for three-level and two-level atomic systems, interacting with nearly resonant monochromatic fields, under the semiclassical and rotating-wave approximations.     

Effects of cavity damping on the entanglement for a three-level atomic system

Based on the master equation for the density matrix, the dynamics of the entanglement of the three-level atom interacting with single-mode field in a finite-Q cavity are studied. It was found that the cavity damping leads to growing entropy and a strong degradation of the entanglement, therefore the coherence loss and entanglement is very sensitive to any change in the cavity damping parameter.     

Comparing different coordination scenarios in a three-level supply chain system

The consignment stock (CS) policy, independently or coupled with vendor managed inventory (VMI), has been practised by businesses and shown to be profitable. It helps to reduce or eliminate out-of-stock instances caused by fluctuations in demand. CS brings several benefits to collaborating parties. Unlike the two-level supply chain models in the literature, this paper considers a three-level supply chain that consists of a supplier, a vendor and a buyer with CS policy agreements. The paper also examines four coordination scenarios (a combination of traditional and CS) in conjunction with a payment scheme between adjacent parties. Nine coordination cases (models) are provided. A sensitivity analysis is performed to study the effects of some parameters on the performance of the developed models. Most of the results showed that a combination of traditional and CS policies returned a higher total system profit.     

Degree of polarization in tightly focused optical fields

We analyze the degree of polarization of random, statistically stationary electromagnetic fields in the focal region of a high-numerical-aperture imaging system. The Richards-Wolf theory for focusing is employed to compute the full 3 x 3 electric coherence matrix, from which the degree of polarization is obtained by using a recent definition for general three-dimensional electromagnetic waves. Significant changes in the state of partial polarization, compared with that of the incident illumination, are observed. For example, a wave consisting of two orthogonal and uncorrelated incident-electric-field components produces rings of full polarization in the focal plane. These effects are explained by considering the distribution of the spectral densities of the three electric field components as well as the correlations between them.     

Focusing and defocusing dynamics of weak-light beam in a resonant three-level atomic system

Focusing and defocusing dynamics of weak-light ring-shaped beams in a Λ-type atomic system are investigated. It is found that focusing of weak light is possible due to the quantum interference effect. The focusing or defocusing regime with vanishing absorption can be manipulated by adjusting detunings from the resonant transition. When the fields are tuned appropriately larger than resonant frequencies, the beam propagates in the defocusing regime and diffraction of the beam takes place. Conversely, the beam focuses in the medium when the laser frequencies are tuned smaller than the resonant frequencies.     

Positive and negative dispersion in a three-level Λ system driven by a single pump

We extend our previous study of a nearly degenerate Λ three-level system that exhibits population trapping when driven by a single pump and produces an absorption or gain doublet in the probe absorption spectrum. In particular, we show that the probe dispersion is positive or negative between the doublet lines, and can survive Doppler broadening. For certain values of the pump Rabi frequency, the sign of the dispersion can be changed by altering the ratio of the splitting between the lower levels to the Doppler width.     

Characterizing polarization management in a p-HMPD system

It has been a common challenge to operate optical see-through head-mounted displays in well-lit environments due to the low image brightness and contrast compared with the direct view of a real-world scene. This problem is aggravated in the design of a see-through head-mounted projection display (HMPD) in which the projected light is split twice by a beam splitter and further attenuated greatly by a retroreflective screen. A polarizing head-mounted projection display (p-HMPD) design was recently proposed to enhance the overall flux transfer efficiency and thus increase the brightness and contrast of displayed images. Different from the conventional nonpolarizing HMPD designs, the light polarization states in the p-HMPD system are deliberately manipulated to maximize the flux transfer efficiency, which can potentially result in three times higher efficiency than that of a nonpolarizing HMPD. By measuring the Mueller matrices of the major elements in both a p-HMPD and a nonpolarizing HMPD, we characterize the polarization dependence of each element on incident angles and wavelengths, and also investigate the depolarization effect of the retroreflective screen. Based on these experimental results, we further examine the overall luminance efficiencies of the two types of systems and analyze how various aspects of display performances are affected by the angular and chromatic dependence of the polarization components.     

Phase control of gain and dispersion in an open V-type system

The control role of the relative phase between the probe and driving fields on gain, dispersion and populations in an open V-type three-level system with spontaneously generated coherence is studied. The result shows that by adjusting the value of the relative phase, the transformation between lasing with inversion and lasing without inversion (LWI) can be realized and high dispersion (refractive index) without absorption can be obtained. The shape and value range of the dispersion curve are similar to those of the gain curve, and this similarity is closely related to the relative phase. The effects of the atomic exit and injection rates and the incoherent pump rate on the control role of the relative phase are also analysed. It is found easier to get LWI by adjusting the value of the relative phase using the open system rather than the closed system, and using an incoherent pump rather than without using the incoherent pump. Moreover the open system can give a larger LWI gain than the closed system.     

Controlled stochastization of oscillations in a chaotic delayed-feedback system

A mathematical model of the ring autooscillatory system, which possesses chaotic dynamics and comprises a nonlinear amplifier with a differentiating element in the feedback chain, a nonlinear oscillatory circuit, and a delay line, is considered. Numerical analysis has been performed for irregularly varying initial conditions. These conditions were set by the solutions of equations describing chaos that simulated intrinsic noises of a real autooscillatory system. It is shown that the irregularly varying conditions of excitation can lead to stochastization of the chaotic oscillations, in which case the oscillatory process becomes irreproducible.     

Two-color bright solitons in a three-level atomic system in the cascade configuration

We investigate two-component spatial optical solitons in a cascaded three-level atomic system. We derive an existence curve in the parameter space of power and spatial widths that reveals the existence of a plethora of coupled solitons. These solitons can exist with two different frequencies and also with two different widths. Our analytical results have been verified by direct numerical simulations. Stability analysis confirms that these solitons are stable.