• Y. Pinhasi, Yu. Lurie, G.A. Pinhasi, A. Yahalom
  CJS, Ariel

Microwave tubes and free-electron lasers are based on distributed interaction between electromagnetic radiation and gain media. When such devices are operating in an amplifier configuration, a forward wave is amplified while propagating in a polarized medium, in a stimulated emission process. Formulating a coupled mode theory for excitation of both forward and backward waves in a distributed gain medium, we have identified in previous works [1] conditions leading to efficient excitation of backward wave without any mechanism of feedback or resonator assembly. The induced polarization is given in terms of an electronic susceptibility tensor, resulting in a coupling coefficient betweens the waves. In this work we extend our previous results in two directions: 1. We discuss the case of a complex coupling coefficient between the backward and forward waves and extend our previous results with respect to a real coupling coefficient, thus the present work discusses a more general and realistic case. 2. We discuss the solution of the same problem relaxing the "high gain" assumption. This leads to a more complex set of third order differential equations.

[1] "Backward Wave Excitation and Generation of Oscillations in Distributed Gain Media and Free-Electron Lasers in the Absence Of Feedback" the 26th International FEL Conference, Trieste, Italy.