130,745 research outputs found
Co-propagating Bose–Einstein condensates and electromagnetic radiation: formation of mutually localized structures
No full textA semi-classical model is derived for describing the interaction between coherent electromagnetic radiation and a Bose-Einstein condensate in the limit of zero temperature, including the back action of the atoms on the radiation. This model is used to analyse the problem of the self-consistent evolution of a laser beam and a BEC atomic beam. The mutual propagation is studied numerically and demonstrates not only the possibility of a stationary regime of mutual guiding, but also of generating a collapse-like phenomenon
Multi–hump soliton–like structures in interactions of lasers and Bose–Einstein condensates
No full textLandau-type damping in nonlinear wavepacket propagation
No full textA modulational instability analysis is carried out for a new kind of integro-differential nonlinear Schrodinger equation which describes nonlinear wave-envelope propagation for several different situations, such as the transport of very intense charged-particle beams in accelerating machines, large amplitude electromagnetic wavepacket propagation in nonlinear media (optical fibres, plasmas, etc.), Langmuir-wave-envelope propagation in warm plasmas, and collective dynamics in mesoscopic physics. The modulational instability analysis is extended from configuration space into phase space, by using the Wigner transform. It is shown that the propagation of a wavepacket in a nonlinear medium, governed by the above nonlinear Schrodinger equation, can be described, in phase space, in terms of a kinetic-like theory similar to the one based on the Vlasov equation which is used for describing both collective plasma dynamics and collective longitudinal dynamics of charged-particle beams in accelerating machines. Remarkably, the phenomenon of Landau damping is recovered for the longitudinal charged-particle beam dynamics (extending in this way a previous analysis carried out within the Thermal Wave Model [R. Fedele and G. Miele, Il Nuovo Cim. D13, 1527 (1991)]) but is also predicted for other physical situations concerning electromagnetic nonlinear wave envelope propagation and mesoscopic physics. Furthermore, the concept of a coupling impedance associated with the wavepacket propagation is also introduced in analogy to the one of charged-particle bunches. This approach provides stability charts fully similar to the ones describing charged-particle beams in accelerating machines. These new results generalize the conventional theory of the modulational instability associated with the nonlinear Schrodinger equation and show clearly the stabilizing role of Landau damping during the development of the modulational instability
How the coherent instabilities of an intense high-energy charged-particle beam in the presence of nonlocal effects can be explained within the context of the Madelung fluid description,
No full textA hydrodynamical description of coherent instabilities that take place in the longitudinal dynamics of a charged-particle coasting beam in a high-energy accelerating machine is presented. This is done within the framework of the Madelung fluid picture provided by the Thermal Wave Model. The well known coherent instability charts in the complex plane of the longitudinal coupling impedance for monochromatic beams are recovered. The results are also interpreted in terms of the deterministic approach to modulational instability analysis usually given for monochromatic large amplitude wave propagation governed by the nonlinear Schrödinger equation. The instability analysis is then extended to a non-monochromatic coasting beam with a given thermal equilibrium distribution, thought of as a statistical ensemble of monochromatic incoherent coasting beams ("white" beam). In this hydrodynamical framework, the phenomenon of Landau damping is predicted without using any kinetic equation governing the phase space evolution of the system
Co-propagating Bose-Einstein condensates and electromagnetic radiation: Emission of mutually localized structures
No full textWe have studied the details of the formation of mutually guided and localized structures of co-propagating coherent electromagnetic radiation and a Bose-Einstein condensate (BEC). In the limit of zero temperature and large detuning, we have used a semiclassical model based on Maxwell equations coupled to the Schrödinger equation which includes the back action of the atoms on the radiation. Following numerically the two systems, we have found that a variety of effects can be displayed depending on the initial conditions: The formation of single-hump mutually guided structures of atoms and radiation seems to be only one of the possible outcomes of the interaction. Other effects we have observed via numerical simulations are, for instance, the creation of atom-laser solitarylike structures which are then symmetrically ejected from the initial central peak or similar symmetrical structures trapped in a bound state and thus oscillating about the central point in a way somehow reminiscent of purely nonlinear optics effect.<br/
A tutorial presentation of the two stream instability and Landau damping
No full textA tutorial presentation is given of the interaction between a high frequency electrostatic wave and a plasma. The analysis is carried out in several consecutive simple steps, starting from electrostatic plasma waves in a cold plasma and successively introducing complications like streaming electrons, the two stream instability and eventually the Landau damping phenomenon. The analysis is based only on cold plasma fluid theory and does not involve kinetic Vlasov theory. (C) 2001 American Association of Physics Teachers
Interacting laser and Bose-Einstein-condensate atomic beams: Mutual guiding structures
No full textA basic set of equations describing the interaction of a Bose-Einstein condensate (BEC) with a laser field is derived based on a semiclassical model and applied to the problem of mutual guiding of laser and BEC atomic beams. Within this framework we have studied stationary spatially localized solutions of the nonlinear system which describe possible laser and BEC atomic beam guiding and have shown their stability as well. It is also shown that a self-guiding effect can be realized through both single- and multiple-scaled structures of a BEC atomic and a laser bea
Propagation of partially incoherent light in nonlinear media via the Wigner transform method
No full textThe propagation of partially incoherent light in nonlinear media is analyzed using the Wigner transform method. The power and versatility of this approach is illustrated by several examples which clearly demonstrate how partial incoherence tends to suppress coherent instabilities by weakening the nonlinearity. In particular, it is found that the effect of partial incoherence on modulational instabilities can be described in terms of a Landau-like damping effect, which counteracts the coherent growth rate of the instability. Similarly, in the case of the self-focusing collapse instability, the nonlinear focusing effect becomes successively smaller as the coherence length of the light decreases and eventually no collapse phenomenon occurs
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