Train Of Micro-Bunches In An Active Medium

We develop explicit expressions for the energy exchange occurring as a train of micro-bunches traverses an active medium. Having the bunch modulated, causes an inherent selection process associated with harmonics of the fundamental frequency in addition to the inherent selection associated with the narrow bandwidth of the medium's resonance. It is demonstrated that for 1010, 70MeV electrons in a 1psec long pulse modulated in a wiggler by a CO2 laser, an increase of a less than 10% percents in the kinetic energy is anticipated provided that at resonance 1kJ/m3 of energy density is stored in the CO2 mixture