Self-consistent quantum electrodynamic calculation of spontaneous emission and small-signal gain in high-voltage free-electron lasers
Abstract
A self-consistent QED (SCQED) theory of spontaneous emission of radiation and single-photon small-signal gain (SSG) is developed for FELs using the Weisskopf-Wigner method. The results agree with existing experimental data on both the line broadening and the line shift and to a reasonable extent with the measured gain. It is shown that the spontaneous-emission spectrum obtained from classical or conventional FEL theories is valid only in the limit of a short undulator that contains a small number of periods. The SSG derived from the SCQED theory is shown to reduce to Colson's (1977) gain formula in the classical limit. However, the SCQED theory predicts significant reductions in the SSG that agree well with the ACO gain data and are not predicted well by Colson's formula. It is discovered that a fundamental physical gain limit exists that is universal to all types of FELs within the limits of the single-photon transition scheme considered.
- Publication:
-
Journal of the Optical Society of America B Optical Physics
- Pub Date:
- October 1990
- DOI:
- 10.1364/JOSAB.7.002061
- Bibcode:
- 1990JOSAB...7.2061C
- Keywords:
-
- Electrodynamics;
- Free Electron Lasers;
- Quantum Theory;
- Spontaneous Emission;
- Amplification;
- Electron States;
- Laser Applications;
- Photons;
- Lasers and Masers