Free Electron Lasers

Abstract

The sections in this article are Electron Kinematics: Resonance and Synchronism Conditions Classical Electron Dynamics Dynamics and Gain in Interfering Two‐Wiggler Fels Quantum Regime of FEL FEL Experimental Parameters Applications Perspectives

Broadband optical gain via interference in the free electron laser: Principles and proposed realizations

“…14 Hz values for optical wigglers with submicron periods [2][3][4]. (2) with electron velocity spread ∆vz = 5c/LW (kL + kW ).…”

“…Free-electron lasers (FELs) convert part of the kinetic energy of nearly-free relativistic electrons into coherent radiation [1][2][3][4]. They can be of two types: 1) devices wherein the electrons are accelerated in a spatially periodic magneto-static, electrostatic, or electromagnetic field, called a wiggler or an undulator; 2) devices wherein the electrons are unperturbed, but instead the laser wave is subject to dispersion, as in Cherenkov transition radiation.…”

“…This results in an antisymmetric dependence of the small-signal standard gain G st on the deviation of the electron velocity v from the resonant velocity v r . Such dependence has been thought to be a fundamental consequence of the Madey gain-spread theorem [1][2][3], which states that the gain lineshape is antisymmetric, since it is proportional to the derivative of the symmetric spontaneous-emission lineshape, which is a sinc 2 function of (v − v r ). This gain lineshape allows for net gain only if the initial velocity distribution is centered above v r , which is often called momentum population inversion.…”

“…In other words, this gain lineshape restricts the momentum spread to values comparable with the width of the positive (gain) part of G st in order to achieve net gain. This width severely limits the FEL gain performance at short wavelengths [2][3][4].…”