S. Pagnutti

Nonlinear harmonic generation in high-gain free-electron lasers

We reconsider the derivation of semianalytical expressions providing the most significant aspects of the high-gain free-electron laser dynamics. We obtain new expressions for the growth of the laser power, of the e-beam-induced energy spread, and of the higher-order nonlinearly generated harmonics. The procedure we employ, based on theoretical ansatz and fitting methods, allows the determination of crucial quantities like the expected harmonic output power and its dependences on the e-beam parameters.

Pulse propagation and nonlinear harmonic generation in free electron laser oscillators

In this paper we present an analysis of the intracavity harmonic generation in free electron laser amplifier operating with short pulses. Various features are investigated. We discuss, in particular, the dependence of the harmonic power and of the width of the associated pulses on the cavity mismatch. It is shown that very short and robust pulses can be generated by suitably setting the cavity desynchronism.

Free electron laser oscillators with tapered undulators: Inclusion of harmonic generation and pulse propagation

We review the theory of free-electron laser (FEL) oscillators operating with tapered undulators. We have considered the case of a uniform tapering and introduced a parameter which characterizes the effect of the tapering on the gain and the saturation intensity. We have analyzed the effect of the tapering on the FEL dynamics by including the pulse propagation effects. We further analyze the importance of tapering as a tool to model the optical pulse shapes and to control the higher harmonic intensities.

High gain oscillators: Pulse propagation and saturation

Semianalytical formulas have been used to model the pulse propagation dynamics of low gain free electron laser oscillators. Most of the scaling relations, including pulse propagation effects, are limited to the low gain regime. We discuss the problem of oscillator devices operating with small signal gain coefficients larger than 1. We comment on the relevant physical aspects and show that gain and saturated power can be reproduced by a set of simple formulas, analogous to those employed for the low gain case.

Theory of high gain free-electron lasers operating with segmented undulators

The dynamical behavior of high gain free-electron lasers, operating with segmented undulators in the self-amplified spontaneous emission regime, is studied using a set of semianalytical formulas, which reproduce the induced energy spread, the bunching coefficients, and the field evolution along the longitudinal coordinate. The proposed technique is applied to the design of segmented free-electron laser devices, employing undulators with helical or linear polarization. The case of biharmonic sections is discussed too, as well as the possibility of extending the analysis to this “exotic” case.

Ontogenetic tumor growth and evolution equations

We review the theory of ontogenetic tumor growth by discussing different evolution equations which account for the relevant dynamics. It is shown that most of the equations proposed can be treated from a unitary point of view. We extend the West ontogenetic evolution model to cancer growth and show that the relevant predictions agree with the experimental data from breast and prostate cancer. We finally prove that aging effects can be easily included in the theoretical scheme proposed.

Introduction to the Physics of Free Electron Laser and Comparison with Conventional Laser Sources

This report is a primer introduction on the sources of coherent syncrotron radiation from FELs compared to conventional lasers. Even though the underlying mechanisms are different, FELs can be considered a laser source to all effects. In fact FEL is based on the stimulated emission of virtual photons by a relativistic electron beam, passing through an undulator/wiggler, much like conventional lasers exploit the stimulated emission by an atomic/molecular system on which a population inversion has been realized. FEL operation is illustrated by means of the usual set of parameters (gain, saturation intensity...) used to describe the functioning of conventional lasers.

Intracavity harmonic generation in figure-8 undulator free electron lasers

We consider a free electron laser oscillator employing an exotic undulator provided by a figure-8, a device having the orthogonal field component oscillating with a period one-half of the radial component. The harmonic spectrum of such an oscillator device is fairly reach. We have indeed emission on odd and even harmonics with orthogonal polarizations. The intracavity nonlinear coherent harmonic generation follows the harmonic undulator spectrum and in addition allows the possibility of obtaining robust and very short pulses at different wavelengths.

The FEL SASE operation, bunch compression and the beam heater

Abstract We discuss the conditions required for an optimal SASE FEL operation when bunch compression techniques are exploited to enhance the bunch peak current. We discuss the case of velocity bunching and magnetic bunch compression. With reference to the latter technique we provide a quantitative estimate of the amount of laser heater power necessary to suppress the micro-bunching instability without creating any problem to the SASE dynamics.

High gain amplifiers: Power oscillations and harmonic generation

We discuss the power oscillations in saturated high gain free electron laser amplifiers and show that the relevant period can be written in terms of the gain length. We use simple arguments following from the solution of the pendulum equation in terms of Jacobi elliptic functions. Nontrivial effects due to nonlinear harmonic generation and inhomogeneous broadening are discussed too, as well as the saturated dynamics of short pulses.