1,721,005 research outputs found
Density matrix approach for quantum free-electron lasers
Get PDFThe density matrix in the Lindblad form is used to describe the behavior of the Free-Electron Laser (FEL) operating in a quantum regime. The detrimental effects of the spontaneous emission on coherent FEL operation are taken into account. It is shown that the density matrix formalism provides a simple method to describe the dynamics of electrons and radiation field in the quantum FEL process. In this work, further insights on the key dynamic parameters (e.g., electron populations, bunching factor, radiation power) are presented. We also derive a simple differential equation that describes the evolution of the radiated power in the linear regime. It is confirmed that the essential results of this work agree with those predicted by a discrete Wigner approach at practical conditions for efficient operation of quantum FELs
The quantum free electron laser: A new source of coherent, short-wavelength radiation
No full textA Free Electron Laser (FEL) operating in the quantum regime can provide a compact and monochromatic Xray source. Here we review the basic principles of a high-gain quantum FEL starting from noise, with special emphasis on the self-amplified spontaneous emission (SASE) mode of operation. In the first part of the paper, a condition for the neglect of the fermionic character of the electrons is derived and the full quantum theory of the N-particle and single-radiation-mode FEL Hamiltonian is presented. Quantum effects such as cooperative gain, discrete spectrum and line narrowing are described, both in the multi-particle and in the second quantization formalism. In the second part, propagation effects (i.e. slippage) are described and the main features of the quantum SASE regime are discussed. The broad and spiky radiation spectrum observed in classical SASE reduces in the quantum regime to a series of narrow lines, associated with sequential transitions between adjacent momentum states. A simple interpretation of the discrete nature of the spectrum and of the linewidth of the single spike observed in the quantum regime is presented
Superradiant light scattering and grating formation in cold atomic vapours
Get PDFA semi-classical theory of coherent light scattering from an elongated sample of cold atoms exposed to an off-resonant laser beam is presented. The model, which is a direct extension of that of the collective atomic recoil laser, describes the emission of two superradiant pulses along the sample's major axis simultaneous with the formation of a bidimensional atomic grating inside the sample. It provides a simple physical picture of the recent observation of collective light scattering from a Bose-Einstein condensate [Science 285 (1999) 571]. In addition, the model provides an analytical description of the temporal evolution of the scattered light intensity which shows good quantitative agreement with the experimental results of Inouye et al
Dispersive optical bistability in cold atomic vapours
No full textWe present an analysis of dispersive optical bistability in a system of cold atoms enclosed in a bidirectional ring cavity. This analysis is carried out using a system of equations which extend the so-called Maxwell-Bloch model to self-consistently include atomic centre-of-mass motion. When the atomic sample is sufficiently cold and dense, the atomic centre-of-mass motion causes the low pump transmission state to become unstable when the pump is blue-shifted with respect to the atomic resonance. This recoil-induced instability results in the exponential growth of the radiation field counterpropagating to the pump and an atomic density grating. The density grating strongly influences the dispersive properties of the atomic sample and causes the pump transmission to jump from the low transmission state to the high transmission state. It is expected that these effects should be observable in a cold (T K), dense (n similar to 10(11) cm(-3)) sample of Rb, enclosed in a high quality ring cavity (R approximate to 99%). (C) 2001 Elsevier Science B.V. All rights reserved
Classical and quantum collective recoil lasing : a tutorial
Get PDFCollective atomic recoil lasing (CARL) is a process during which an ensemble of cold atoms, driven by a far-detuned laser beam, spontaneously organize themselves in periodic structures on the scale of the optical wavelength. The principle was envisaged by R. Bonifacio in 1994 and, ten years later, observed in a series of experiments in Tübingen by C. Zimmermann and colleagues. Here, we review the basic model of CARL in the classical and in the quantum regime
The semiclassical and quantum regimes of super-radiant light scattering from a Bose-Einstein condensate
No full textWe show that many features of the recent experiments of Schneble et al (2003 Science 300 475), which demonstrate two different regimes of light scattering by a Bose-Einstein condensate, can be described using a one-dimensional mean-field quantum CARL model, where optical amplification occurs simultaneously with the production of a periodic density modulation in the atomic medium. The two regimes of light scattering observed in these experiments, originally described as 'Kapiza-Dirac scattering' and 'super-radiant Rayleigh scattering', can be interpreted as the semiclassical and quantum limits respectively of CARL lasing
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Coupled nonlinear optical-BEC dynamics
No full textThe system is described using a set of coupled Maxwell-Gross-Pitaevskii equations which describe the evolution of the condensate under the influence of optically-induced forces, coupled with the evolution of the optical fields driven by the condensate. New results obtained using this model including the effect of the wave-like nature of the atoms and atom-atom collisions on the CARL (collective atomic recoil laser) instability are presented
The detrimental effect of spontaneous emission in quantum free electron lasers : a discrete Wigner model
Get PDFWe study the spontaneous emission in high-gain free-electron lasers operating in the quantum regime and its detrimental effect on coherent emission. A quantum model describing the coherent and spontaneous emission in free electron lasers has been recently proposed and investigated [G. R. M. Robb and R. Bonifacio, Phys. Plasmas 19, 073101 (2012)]. The model is based on a Wigner distribution describing the electron beam dynamics, coupled to Maxwell equations for the emitted radiation field. Here, we rephrase the model in a more rigorous way, considering a discrete Wigner distribution defined for a periodic space coordinate for which the electron momentum is discrete. From its numerical solution, we find good agreement with the approximate continuous model. In the quantum regime of the free-electron laser, we obtain a simple density matrix equation for two momentum states, where the role of the spontaneous emission has a clear interpretation in terms of coherence decay and population transfer
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