Threedimensional simulations of harmonic radiation and harmonic lasing
Abstract
Characteristics of the harmonic emission from free electron lasers (FELs) are examined in the spontaneous, coherentspontaneous and stimulated emission regimes. The radiation at both odd and even harmonic frequencies is treated for electron beams with finite emittance and energy spread. In the spontaneous emission regime, the transverse radiation patterns including the transverse frequency dependences, are given. How this expression is modified to include energy spread and emittance is described. In the coherentspontaneous emission and stimulated emission regimes, the interaction of the radiation fields with the electrons must be treated self consistently. Here, a single frequency distributed transverse source function for each electron is used in the harmonic version of the 3D code FELEX to model the harmonic radiation. The code has recently been modified to simultaneously model the fundamental and harmonic interactions for multiplepass oscillator simulations. These modifications facilitate the examination of FELs under various operating conditions. When the FEL is lasing at the fundamental, the evolution of the harmonic fields can be examined. This evolution is unique in the sense that the electron beam radiates at the harmonic frequencies in the presence of the harmonic radiation circulating in the cavity. As a result, enhancements of the harmonic emission can be observed. Finally, harmonic lasing can occur in cases where there is sufficient gain to overcome cavity losses and lasing at the fundamental can be suppressed. The characteristics and efficiency of these interactions are explored.
 Publication:

Presented at the 12th International Free Electron Laser Conference
 Pub Date:
 1990
 Bibcode:
 1990ifel.conf...17S
 Keywords:

 Computerized Simulation;
 Free Electron Lasers;
 Harmonic Radiation;
 Lasing;
 Three Dimensional Models;
 Electron Beams;
 Frequencies;
 Harmonic Generations;
 Radiation Distribution;
 Lasers and Masers