Coherent Radiation Field Research Articles

Multistability in mesoscopic Rydberg-atom systems.

We describe a system of N two-level Rydberg atoms which travel through a resonant cavity and interact with a single mode of the resonator. N is assumed to be on the order of a few tens or hundreds of atoms. In particular, we analyze the case where the atoms are injected to the lower state (absorber) and the system is driven by an external coherent radiation field exactly resonant with the atoms and with the cavity. In the case of a monoenergetic atomic beam, the picture that arises is substantially different from that of standard optical bistability. The switching behavior is not governed by saturation, but by the Rabi cycles of the atoms in the cavity. The hysteresis cycle of the population of the upper level is butterfly shaped. When the bistability parameter exceeds an appropriate second threshold, the system displays multistability rather than simple bistability, and under proper conditions it develops domains of instability in positive-slope regions of the steady-state curve. We analyze the effects of a velocity distribution (thermal or Gaussian) in the atomic beam, and of inhomogeneous broadening caused by stray electric fields. Finally, we discuss the feasibility of an experimental observation of the effects predicted by our analysis.

Erratum: Quantum chaos in interactions of multilevel quantum systems with a coherent radiation field [Sov. Phys. Usp. 35, 303–326 (April 1992)

Erratum: Quantum chaos in interactions of multilevel quantum systems with a coherent radiation field [Sov. Phys. Usp. 35, 303–326 (April 1992)

Quantum chaos in interactions of multilevel quantum systems with a coherent radiation field

Studies on the dynamics of multilevel quantum systems in a coherent radiation field are reviewed. Major attention is paid to phenomena of quantum nonlinear resonance and the interaction of two quantum nonlinear resonances, and also to the analysis of the real physical systems where these phenomena are realized.

Glauber-Lachs version of the Jaynes-Cummings interaction of a two-level atom.

The dynamics of the Jaynes-Cummings interaction of a two-level atom interacting with a single mode of a radiation field prepared in a Glauber-Lachs state is investigated to study the development of seemingly chaotic oscillations of the atomic inversion from a regular collapse-and-revival phenomenon, as the field statistics is changed from the coherent state to the thermal state. The effect of thermal photons on the coherent light is shown to be striking: Both the photon distribution as well as the atomic inversion are highly sensitive to even a very small addition of thermal photons to an initially coherent radiation field. We also compare the collapse and revival occurring in the micromaser case with the Glauber-Lachs version of the Jaynes-Cummings model.

Квантовый хаос при взаимодействии многоуровневых квантовых систем с полем когерентного излучения

Квантовый хаос при взаимодействии многоуровневых квантовых систем с полем когерентного излучения

Numerical modeling of coherent coupling and radiation fields in planar Y-branch interferometers

The beam-propagation method is used to study intermodal power transfer and radiation losses in slab waveguide splitters and combiners. Numerical computations demonstrate how modal power at an interferometer's recombination point exhibits an oscillatory dependence on the length of each distinct section of the structure. Recoupling of guided and unguided modes can be anticipated and adjusted so as to maximize output modal power and minimize sensitivity to transition lengths. Examples are given for systems formed from both angle bends and S bends.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Laser pulse sequence effects on selective ionization in three-level systems driven by coherent radiation fields

Using the time-dependent Schrodinger equation we investigate the effect of different pulse sequences of two lasers on selective ionization in three-level systems driven by coherent radiation fields. It is assumed that inhomogeneous broadening as well as the radiative decay can be neglected during the laser pulses. We demonstrate to what an extent the selectivity given by the absorption or relaxation process can be increased by coherent interaction during the first step and different timing of the incoherent interaction during the second step of a two-step photoionization. A comparison is made with the rate-equation results. We could show that utilization of coherent excitation for high ionization selectivity is most efficient if the two laser pulses do not overlap.

Light Squeezing in the Jaynes-Cummings Model with Intensity-dependent Coupling

Abstract We have found that in the intensity-dependent-coupling Jaynes-Cummings model with the coherent radiation field light squeezing exhibits periodical revivals. The influence of the initial states of the atom on the squeezing of light is investigated in detail.

Ion cyclotron emission from energetic fusion products in tokamak plasmas—A full-wave calculation

A full-wave ion cyclotron resonant heating (ICRH) code has been modified to allow calculation of cyclotron emission from energetic ions in tokamaks. The immediate application is to fusion alpha particles in near-ignition devices. This permits detailed evaluation of proposed alpha particle diagnostics [Proceedings of the Thirteenth European Conference on Controlled Fusion and Plasma Heating, Schliersee, Federal Republic of Germany, 1986, edited by G. Briffod and M. Kaufmann (European Physical Society, Petit-Lancy, Switzerland, 1986), Part 1, Vol. 2, p. 37.] This full-wave approach automatically takes into account wall reflections, standing waves, and plasma absorption and overcomes the difficulties inherent in attempting to apply conventional geometrical optics to long wavelengths. By calculating the coherent radiation field caused by an ensemble of localized current sources (and retaining the phase information), the directivity of pickup antennas is correctly represented. This method also promises to be useful for studying other kinds of plasma radiation, such as that produced by instabilities.

Reduction of sidelobe and speckle artifacts in microwave imaging: the CLEAN technique

Large random thin arrays provide a high angular resolution microwave images but are plagued with artifacts (false targets and target breakup or speckle) caused by high sidelobe levels. The CLEAN algorithm for reducing the sidelobe-induced artifacts is extended to the coherent radiation field and the theory placed on a quantitative basis. The CLEAN technique decomposes the received echoes of a coherent multiple-target scene by iterative cancellation of the largest target found. At each step, cancellation information is used to create a target image. The image includes target intensities, phases, and directions. The process is designed for an imaging instrument consisting of a random thinned array. A condition is derived which, when satisfied, guarantees that all proper targets will be preserved in the cleaned image and all false targets discarded. An algorithm involving moving thresholds is derived to extract the target coordinates. It is shown that targets much weaker than the sidelobe level can be detected and displayed without the hazard of artifacts. The target dynamic range and the image contrast can be increased by up to twice the signal-to-noise ratio per element. >

Ground-state coherence induced oscillations in a three-level system

The interaction of a three-level atomic medium with two degenerate sublevels in the ground-state with a coherent radiation field in a ring cavity is investigated. We pay specific attention to atomic coherence within the ground-state doublet, considering separate decay rates for the ground-state coherence and the population difference. In a previous paper we presented the stationary solutions and here we report on self-pulsing solutions. At critical intensities of the input field, the partially stable symmetry-breaking branches give rise to Hopf bifurcations. Furthermore, we observe in a limiting case of the limit cycles solitary solutions. The associated diverging periods show an interesting power law behaviour.

Quantum chaos: diffusion photoeffect in hydrogen

Some properties of quantum chaos G P Berman Stochastic web and structure generation G M Zaslavski, Renad Z Sagdeev, O A Usikov et al. Dynamical chaos in magnetic systems K N Alekseev, G P Berman, V I Tsifrinovich et al. Quantum chaos in interactions of multilevel quantum systems with a coherent radiation field G P Berman and A R Kolovski Minimal chaos, stochastic webs, and structures of quasicrystal symmetry G M Zaslavski, Roal'd Z Sagdeev, D A Usikov et al. Ionization of excited hydrogen atoms by microwave fields: a test case for quantum chaos R Blumel and U Smilansky Quantum effects in the long time behavior of the dissipative standard map T Dittrich and R Graham Quantum chaos: diffusion photoeffect in hydrogen

Four-wave mixing using partially coherent fields in systems with spatial correlations.

A microscopic correlation function expression for the signal in four-wave mixing is developed. Both stationary and transient (i.e., photon-echo) experiments with coherent or incoherent radiation fields are considered. In general, these observables are described by an eight-point correlation function of the dipole operator involving two particles, and the signal cannot be written as an amplitude squared. Conditions under which the correlation function may be factorized into a product of two four-point, single-particle correlation functions are specified. In this case the conventional approach, based on calculating a nonlinear polarization and substituting it as a source in Maxwell's equations, is justified. However, in the presence of long-range spatial correlations in the sample (e.g., near critical points) the conventional formulation breaks down and the present theory should be used.

Transitions from coherent to incoherent state induced by anharmonic interaction

A non-linear stochastic oscillator driven by a coherent radiation field is studied. Analog simulation is shown to support the arguments of theory on the specific role of the fluctuation-dissipation process and/or anharmonic interaction in making valid a treatment in terms of a Boltzmann-like distribution of energy. The results of analog simulation show that at certain values of the excitation frequency a superimposition of a coherent and an incoherent state may appear thereby opening the way to a more exhaustive theoretical treatment of this problem.

Optical multistability and ground-state coherence in a three-level system

The interaction of a three-level atomic medium with two degenerate sublevels in the ground state with a coherent radiation field in a ring cavity is investigated. We pay specific attention to atomic coherence within the ground-state doublet, and introduce separate decay rates for the ground-state coherence and the population difference. If the atomic density exceeds a critical value, the system exhibits “symmetric bistability”. In addition, in certain regions of parameter space we find symmetry-breaking branches, yielding optical multistability. We propose physical mechanisms for the symmetric as well as for the symmetry-breaking instability.

Diffusion of electrons in a gas in the field of an intense coherent radiation.

A theory of electron diffusion in a gas in the presence of an intense radiation field is presented. The theory is applicable when the classical electron oscillation energy ${\ensuremath{\epsilon}}_{0}$ exceeds the typical electron-gas inelastic collision energy loss \ensuremath{\xi} and when the frequency \ensuremath{\omega} of the wave is much larger than the inelastic collision frequency ${\ensuremath{\nu}}_{\mathrm{coll}}$. It is shown that the existence of these two different time scales allows us to derive a simple Langevin type, model stochastic equation, describing the slow-time-scale electron transport in the gas. Assuming linear dependence of ${\ensuremath{\nu}}_{\mathrm{coll}}$ on the electron energy, simple analytic expressions for the time evolution of the average electron translational energy W and random-walk parameter 〈${x}^{2}$${〉}_{\mathrm{av}}$ are derived. In the long-time limit W=\ensuremath{\xi}/4 and 〈${x}^{2}$${〉}_{\mathrm{av}=\mathrm{Dt}}$, where the diffusion coefficient D is independent of both \ensuremath{\omega} and ${\ensuremath{\epsilon}}_{0}$. These predictions are in a good agreement with the results of Monte Carlo computer experiments, conducted for the cases of ${\mathrm{N}}_{2}$ and Hg.

Quantum-beat spectroscopy with coherent and incoherent radiation fields

The effects of partial or complete incoherence in the radiation field on quantum-beat spectroscopy of intermediate-size molecules are analyzed. A unified expression which interpolates between the coherent and the incoherent limits is derived for a radiation field whose phase undergoes a stochastic random modulation. The quantum-beat pattern is broadened and partially eroded as the degree of incoherence increases, but it does not diappear even in the extreme incoherent case, where simple rate equations apply. The effects of incoherence vanish completely if the excitation pulse has a sufficiently short duration.

Some soluble models for periodic decay and revival

The authors present three analytically tractable models for a two-level atom interacting with a coherent or thermal radiation field and study the behaviour of the atomic excitation energy for various initial conditions.

A generalized three-level Jaynes-Cummings model

A quantum-statistical model for a three-level atom interacting with two initially coherent radiation fields is presented. The mean photon numbers and the mean atomic level occupation, calculated through numerical methods, exhibit novel properties. The case that initially only one mode exists is also considered.

Multidimensional spectroscopy

The quantum states produced by non-linear interaction of a coherent uniform radiation field with dipolar matter are evaluated by a time-dependent perturbation expansion of the density matrix. The non-linear terms of the expansion are Fourier transformed to yield multi-dimensional spectra which indicate the connectivities in the underlying energy level diagrams. The spectra can be measured in experiments with multiple resonance, multiple pulse or stochastic excitation. Although the theory presented is of general validity in coherent spectroscopy, emphasis is placed on its application in non-linear N.M.R. spectroscopy. It illustrates particularly well the common basis of double, 2D correlated and multi-dimensional stochastic magnetic resonance.