Search Results (17 total)

We present a phenomenological treatment of free-electron laser storage ring saturation dynamics. The model includes longitudinal instabilities, Touschek intrabeam scattering, and nonzero off-energy-function contributions. The model predictions are compared with Super ACO experimental results and the agreement is shown to be satisfactory.

Nonlinear harmonic generation can be a very useful and important phenomenon for single-pass free-electron lasers (FELs) operating in the high-gain regime. Strong bunching at the fundamental wavelength and its associated higher harmonic content allow significant radiation at shorter wavelengths to be emitted without serious effects upon the output power at the fundamental. Here, we analyze the relative sensitivities to beam quality variations of the output fundamental and harmonic powers for a visible-wavelength FEL operating in the high-gain regime.

The stabilization of nonlinear excitations by noise is a topic of fundamental importance in many physical problems. We discuss a genuine example within the context of storage ring-free electron laser physics, by presenting a model which allows the characterization of the system evolution and the determination of the conditions leading to the suppression of instabilities of sawtooth type. The conclusions of the model are confirmed by a comparison with experimental results on the Super Aco Storage Ring-Free Electron Laser.

We develop a heuristic dynamical model to analyze the interplay between free-electron-laser (FEL) storage-ring dynamics and instabilities of the head-tail type. We show that, under given conditions, the FEL may inhibit the onset of the instability and may provide a reduction of the electron-beam transverse dimensions. Some experimental results that can be used in support of the model are also reported.

We exploit the Fokker-Planck equation to investigate the longitudinal phase-space dynamics of a FEL amplifier operating with a storage ring. We study both standard and optical-klystron configurations and prove that in both cases the damping times of the electron longitudinal modes are modified by the system operating conditions. In particular, they decrease with increasing laser power when the input laser is tuned at the resonant frequency.

We discuss the storage-ring longitudinal dynamics by including the contributions from a free-electron-laser amplifier and from the microwave instability. We show that the two effects exhibit a mutual interplay that leads, under certain conditions, to the inhibition of the start up of the microwave instability and/or to a reduction of the electron-beam heating due to the free-electron laser. The agreement with the experimental results is also discussed.

The waveguide operation of a compact free-electron laser driven by a 2.3-MeV S-band microtron is reported. Power up to 1 kW in 4-μs pulses has been generated at wavelengths in the range between 2.1 and 2.6 mm. Novel tuning features and temporal characteristics of the emitted radiation, related to the bunched nature of the electron beam and to the dispersive effect of the waveguide, have been observed.

In this Brief Report we propose a simple phenomenological model of gain saturation for free-electron lasers operating with a bunched electron beam. The model is based on an analogy with that of conventional lasers, and in spite of its simplicity, the obtained results are in close agreement with the numerical simulations performed within the context of a more complete theory.

We report the observation of coherent emission from a Cherenkov free-electron laser driven by a 5-MeV radio-frequency microtron. Power up to 50 W in pulses of 4-μs duration has been generated at the wavelengths of 1.6 and 0.9 mm using two different dielectric-loaded waveguides.

In this paper we use a recently suggested analytical solution of the pulse propagation equation in free-electron lasers (FEL) to get further information on the lethargy and on the velocity of propagation of the optical packet. We also introduce a refractive index for the FEL interaction. Finally, the supermodes relevant to the regime of long electron bunch are found analytically and a comparison with earlier numerical results is carried out.

We propose an analytical solution to the propagation equation of the optical pulse both in free-electron lasers and in optical klystrons. Our results include in a natural way the lethargy and wave-packet spreading.

The free-electron laser is described by the self-consistent solution of the coupled system of the Lorentz force equation for the electrons and the Maxwell equation for the laser field. We show that, near saturation and at both low- and high-gain regime, the evolution of each longitudinal mode in the optical cavity can be written as an integral equation. We present numerical solutions of the integral equations for a free-electron-laser oscillator.

We discuss a method to obtain analytical solutions of the evolution equation of the optical signal in long-pulse free-electron-laser oscillators in the low-gain and small-signal regime. Supermodes are identified with the eigenstates, harmonic-oscillator orthonormal functions, of a non-Hermitian Hamiltonian. Inhomogeneous broadening effects due to energy spread and emittance are included. The space-time characteristics of the laser field are obtained with a significant reduction in the computer time.

We discuss a phenomenological one-dimensional, self-consistent, multimode (longitudinal) theory for a free-electron-laser oscillator. A strong fundamental mode and a weak sideband mode are followed through many passes in the optical cavity as the energy of the electron beam decreases monotonically. The time evolution of the laser power exhibits oscillations produced by the sequential growth to saturation and subsequent decay of longitudinal modes evenly distributed in frequency.

In a recent paper of Lee [Phys. Rev. A 31, 1213 (1985)], it was stated that the photon-number distribution in a free-electron laser is always sub-Poissonian. This statement is clearly in contradiction with well-known published results. We show that in the recoilless approximation the photon statistics is Poissonian. However, for electron recoil different from zero, the photon-number distribution presents bunching (antibunching) for positive (negative) detuning parameter.

A preliminary comparison of the fundamental characteristics of undulator and Čerenkov free-electron lasers is presented. It is assumed that both devices are operating in the Compton regime and that they are driven by a short-pulse relativistic electron beam.

This paper presents a fully classical theory of the free-electron laser. The theory is formulated in a moving frame where the pseudoradiation field due to static wiggler magnet is in resonance with the laser field imposed by an optical cavity. The basic amplification process is then one of elastic scattering. In this frame both fields are treated classically, as is the electron motion. When the laser and wiggler fields are taken to be constant during the interaction period, it is shown that the laser operation can be described by the classical pendulum equation. This is used to evaluate the unsaturated gain and momentum distribution. For the saturated situation numerical results are given, which have been obtained by the use of the Jacobi elliptic functions. The new features found are singularities in the momentum distribution and their evolution with intensity, saturation enhancement of the gain and the possibilities of bistability and hysteresis entailed by it, and the possibility of discussing and interpreting the various features in a unified way. Finally, a detailed discussion of the approximations and their validity is given.