101 research outputs found
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
The detrimental effect of spontaneous emission in quantum free electron lasers : a discrete Wigner model
No full textWe 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
Superradiant light scattering and grating formation in cold atomic vapours
No full textA 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
Quantum theory of SASE FEL
No full textWe describe a free-electron laser (FEL) in the Self-Amplified Spontaneous Emission (SASE) regime quantizing the electron motion and taking into account propagation effects. We demonstrate quantum purification of the SASE spectrum, i.e. in a properly defined quantum regime the spiking behavior disappears and the SASE power spectrum becomes very narrow
Density matrix approach for quantum free-electron lasers
No full textThe 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
Propagation effects in the quantum description of collective recoil lasing
No full textThe free electron laser and collective atomic recoil laser (CARL) are examples of collective recoil lasing, where exponential amplification of a radiation field occurs simultaneously with self-bunching of an ensemble of particles (electrons in the case of the FEL and atoms in the case of the CARL). In this paper, we discuss quantum and propagation effects using a model where the particle dynamics are described quantum-mechanically in terms of a matter-wave field, which evolves self-consistently with the radiation field. The model shows that the scattered radiation evolves superradiantly both in the case where the particle ensemble is short compared to the cooperation length of the system, and where the ensemble is long compared to the cooperation length. In both short and long pulse cases there exist a classical and quantum regime of superradiant emission. For short samples in both quantum and classical regimes the superradiant pulse has a low peak intensity and is said to exhibit `weak' superradiance. For long pulses in both quantum and classical regimes of evolution, the dynamics at the rear edge of the sample is dominated by propagation. This produces a,strong' superradiant pulse with much higher peak intensity than that predicted by `mean-field' or `steady-state' models in which propagation effects are neglected. (c) 2005 Elsevier B.V. All rights reserved
Recoil-induced effects in passive and active atomic systems
No full textA theoretical analysis of absorptive optical bistability in a passive atomic medium and bidirectional lasing in an active atomic medium is presented. The atomic medium consists of a collection of cold two-level atoms and the atom-radiation field interaction is described using a one-dimensional semiclassical model. It is shown that when the effects of atomic recoil are included self-consistently, the interaction between the atoms and the radiation can be changed significantly from that when the effects of atomic recoil are neglected
Quantum-fluid description of the free-electron laser
No full textUsing the Madelung transformation we show that in a quantum free-electron laser the beam obeys the equations of a quantum fluid in which the potential is the classical potential plus a quantum potential. The classical limit is shown explicitly
Atomic interaction effects in the superradiant light scattering from a Bose-Einstein condensate
No full textWe investigate the effects of the atomic interaction in the superradiant Rayleigh scattering from a Bose-Einstein condensate driven by a far-detuned laser beam. We show that for a homogeneous atomic sample the atomic interaction has only a dispersive effect, whereas in the inhomogeneous case it may increase the decay of the matter-wave grating
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