Showing papers on "Atomic coherence published in 1998"

Electromagnetically induced transparency

Abstract: The subject of electromagnetically induced transparency (EIT) is reviewed in this paper. Emphasis is placed on the experimental work reported in this field since 1990. Theoretical work is also covered, although it is not intended to review all the very numerous recent theoretical treatments on this topic. The basic physical ideas behind EIT are elucidated. The relation of EIT to other processes involving laser-induced atomic coherence, such as coherent population trapping, coherent adiabatic population transfer and lasing without inversion, is discussed. Experimental work is described covering the following topics: EIT with pulsed and continuous-wave sources, lasing without inversion, pulse propagation in a laser dressed medium and EIT in nonlinear optical processes. A full set of references and a bibliography are included.

Resonant Enhancement of Parametric Processes via Radiative Interference and Induced Coherence

Abstract: Nonlinear optical parametric processes are studied in a resonantly driven multilevel system displaying quantum interference effects. It is shown that in such systems a new regime of nonlinear amplification is possible, in which a pair of correlated Stokes and anti-Stokes fields can be generated from infinitesimally small initial values. An atomic coherence grating emerges during this process of efficient nonlinear amplification. The present analysis explains the results of recent optical phase conjugation experiments involving atomic phase coherence.

Topical review Electromagnetically induced transparency

Abstract: The subject of electromagnetically induced transparency (EIT) is reviewed in this paper. Emphasis is placed on the experimental work reported in this ®eld since 1990. Theoretical work is also covered, although it is not intended to review all the very numerous recent theoretical treatments on this topic. The basic physical ideas behind EIT are elucidated. The relation of EIT to other processes involving laser-induced atomic coherence, such as coherent population trapping, coherent adiabatic population transfer and lasing without inversion, is discussed. Experimental work is described covering the following topics: EIT with pulsed and continuous-wave sources, lasing without inversion, pulse propagation in a laser dressed medium and EIT in nonlinear optical processes. A full set of references and a bibliography are included.

Absorption with inversion and amplification without inversion in a coherently prepared V - system: a dressed state approach

Abstract: Light induced absorption with population inversion and amplification without population inversion (LWI) in a coherently prepared closed three level V - type system are investigated. This study is performed from the point of view of a two color dressed state basis. Both of these processes are possible due to atomic coherence and quantum interference contrary to simple intuitive predictions. Merely on physical basis, one would expect a complementary process to the amplification without inversion. We believe that absorption in the presence of population inversion found in the dressed state picture utilized in this study, constitutes such a process. Novel approximate analytic time dependent solutions, for coherences and populations are obtained, and are compared with full numerical solutions exhibiting excellent agreement. Steady state quantities are also calculated, and the conditions under which the system exhibits absorption and gain with and without inversion, in the dressed state representation are derived. It is found that for a weak probe laser field absorption with inversion and amplification without inversion may occur, for a range of system parameters.

Nonlinear frequency conversion with short laser pulses and maximum atomic coherence

Abstract: A perturbation treatment for Raman generation with a combination of long, short, and delayed laser pulses is presented. When the coupling and probe lasers are applied in a counterintuitive sequence, the fast oscillatory contributions to populations and coherence are eliminated by robust adiabatic passage, allowing a much simpler solution to the problem. Such counterintuitive and on-resonance operation allows effective electromagnetically induced transparency to evolve so that the probe laser photons will experience no absorption yet still fully participate in the nonlinear frequency conversion. Consequently, better conversion efficiency should be possible. {copyright} {ital 1998} {ital The American Physical Society}

Coherence of atomic matter-wave fields

Abstract: In analogy to Glauber's analysis of optical coherence, we adopt an operational approach to introduce different classes of atomic coherence associated with different types of measurements. For the sake of concreteness we consider specifically fluorescence, nonresonant imaging, and ionization. We introduce definitions of coherence appropriate to them, which we call electronic, density, and field coherence, respectively. We illustrate these concepts in various descriptions of Bose-Einstein condensation, showing that each of these descriptions makes different implicit assumptions on the coherence of the system. We also study the impact of elastic collision on the field and density coherence properties of atom lasers.

Nondegenerate four-wave mixing in a double-/spl Lambda/ system under the influence of coherent population trapping

Abstract: The atomic coherence effect can be used in enhancing the efficiencies of nonlinear optical processes. Particularly, nondegenerate four-wave mixing (NDFWM) in multilevel systems has recently gained attention in connection with the advantage of using coherent population trapping (CPT) or electromagnetically induced transparency (EIT) to enhance the efficiency of generated signals. Generally speaking, linear absorption competes with the nonlinear signal generation at the exact one-photon resonance condition. However, the linear absorption can, in principle, be reduced or even eliminated by preparing the system in the CPT or EIT state. We report experimental demonstrations of NDFWM in several multi-level configurations in rubidium atomic vapor. In one of the double-/spl Lambda/ systems an unusual behavior of signal output power as a function of pump power, i.e. a maximum in the generated signal power is reached as the pump power increases, is experimentally observed. By comparing with several related /spl Lambda/ and double-/spl Lambda/ systems, we have concluded that CPT is the mechanism for this interesting effect.

Two-atom laser

Abstract: A theoretical model of a microscopic laser system incorporating two identical atoms coupled to a single resonator mode is investigated in detail. It is established that a dramatic improvement in laser quality results from the addition of a second atom into the cavity. The enhanced laser action, arising from a cavity-induced mutual atomic coherence, is inferred from comprehensive studies of the steady-state and dynamical properties of the cavity output field. Evidence of laser action is also found in the fluorescence field where position-dependent spectral profiles occur. Counterintuitively, we establish that antibunching phenomena in the fluorescence can be enhanced by incoherent pumping.

Atom Interferometers and Atomic Coherence

Abstract: Atom interferometers are powerful tools for the study of fundamental issues in quantum mechanics. This paper describes the use of our atom interferometer [1] for an experimental realization of Feynman's gedanken experiment in which the observation of photons scattered off of particles emerging from a double slit is used to obtain which path information. This determination, in principal, of the particle's path, destroys any interference effects downstream. The interference can be regained by observing only those particles which scatter a photon into a small range of final directions.

Sub-Doppler absorption resonances induced by strong radiation

Abstract: New possibilities are demonstrated for eliminating uncompensated Doppler broadening in different types of nonlinear optical processes by means of atomic coherence effects in strong electromagnetic fields are demonstrated.

The kinetics of the atomic relaxation induced by laser noise

Abstract: We present a theoretical study of strong laser-atom interactions, when the laser field parameters are subjected to random processes. The atom is modelled by a two- and a three-level system, while the statistical fluctuations of the laser field are described by a pre-Gaussian model. The interaction of the laser-target is treated nonperturbatively by using the calculation method based on the Hermitian Floquet theory. Our aim consists in studying the kinetics of atomic relaxation induced by laser noise. In the resonant case with electric field strengths small with respect to the atomic unit electric strength, the present nonperturbative results are in agreement with those obtained within the rotating wave approximation of Eberly et al and Wodkiewicz et al for an atom modelled by a two-level system. We discuss some examples which demonstrate the destruction of atomic coherence by the noise, the regime of relaxation to the equilibrium state and the optical analogue of motional narrowing. We also give new results for two- and three-level systems, and for a strong laser field at exact resonance, in the case of phase, amplitude noises. The case of fluctuation due to collisions is also discussed. Our numerical results indicate that ionization effects, in the presence of laser noise, can lead to important modifications of the populations for strong laser-atom interactions. The changes in the ionization rates generated by the noise are also investigated.

Field oscillations in a micromaser with injected atomic coherence

Abstract: The electric field in a lossless, regularly-pumped micromaser with injected atomic coherence can undergo a period-two oscillation in the steady state. The field changes its value after a single atom passes through the micromaser cavity, but returns to its original value after a second atom travels through. We give a simple explanation for this phenomenon in terms of tangent and cotangent states. We also examine the effect of cavity damping on this steady state.

Enhancing resonant four-wave mixing via dressed inversions

Abstract: We provide additional insight into the process of resonant four-wave mixing via an analysis in the dressed states basis. As opposed to the common situation in lasing without inversion, both the excited and the ground state of the transition with enhanced coherent field generation are coupled to each other via external driving fields. For this reason we find more similarities to the well-understood process of light amplification in driven two-level systems. Initial gain does not need to arise from a spontaneous photon or a probe field but arises due to the coherence established directly by the strong external driving laser fields.

Field Oscillations in a Micromaser with Injected Atomic Coherence

Abstract: The electric field in a lossless, regularly-pumped micromaser with injected atomic coherence can undergo a period 2 oscillations in the steady state. The field changes its value after a single atom passes through the micromaser cavity, but returns to its original value after a second atom travels through. We give a simple explanation for this phenomenon in terms of tangent and cotangent states. We also examine the effect of cavity damping on this steady state.

Enhancement of optical signal modulation by atomic coherence effects

Abstract: We investigate a new approach for the modulation of an optical signal based on the use of atomic coherence to control and enhance the response of the nonlinear medium. We describe a microscopic multi-level model of a medium driven by external fields and probed by a weak signal. We present explicit results describing the stationary behavior of this system, and outline a scheme for the analysis of its time-dependence.

Field and density coherence of matter-wave fields

Abstract: In analogy to Glauber's analysis of optical coherence, we adopt an operational approach to introduce different classes of atomic coherence associated with different types of measurements. For the sake of concreteness we consider specifically fluorescence, nonresonant imaging, and ionization. We introduce definitions of coherence appropriate to them, which we call electronic, density, and field coherence, respectively. We illustrate these concepts in various descriptions of Bose-Einstein condensation, showing that each of these descriptions makes different implicit assumptions on the coherence of the system. We also study the impact of elastic collision on the field and density coherence properties of atom lasers.