Classical freeelectron lasing in an undulating electrostatic field in the axial direction
Abstract
It is shown that the phase of the electromagnetic wave emitted through stimulated emission is intrinsically random. The insensitivity of the phase of the laser field to any disturbance in the laser cavity parameter derives from the fact that stimulated and spontaneous emissions take place concurrently at the same wave vector, the phases of spontaneous emission are mildly bunched, and the central limit theorem can be applied to the phase of the laser field. The two spectral lines observed in the SmithPurcell freeelectron laser experiment show that both classical and quantummechanical freeelectron lasings, in which the wigglers behave as classical waves and wiggler quanta respectively, take place concurrently at different laser wavelengths in the case of the electric wiggler. It is shown that the coherence of the classical freeelectron laser is achieved through modulation of the relativistic electron mass by the electric wiggler. The classical freeelectron lasing is calculated using the quantumaugmented classical theory. In this, the probability of stimulated emission is first evaluated by interpreting the classically derived energy exchange between an electron and the laser field from a quantummechanical viewpoint. Then the laser gain is obtained from this probability by using a relationship between the two quantities derived by quantum kinetics. The wavelength of the fundamental line of classical freeelectron lasing is twice the wavelength of the fundamental line of the freeelectron twoquantum Stark emission, which is the quantum freeelectron lasing in the electric wiggler. The gain of the classical freeelectron lasing appears to scale as λ^{3}_{w}/γ^{3}, where γ is the Lorentz factor of the electron beam and λ_{w} is the wavelength of the wiggler.
 Publication:

Journal of Plasma Physics
 Pub Date:
 April 1992
 DOI:
 10.1017/S002237780002417X
 Bibcode:
 1992JPlPh..47..197K