Electron Cyclotron Resonance Gain in the Presence of Collisions
A cyclotron resonance maser source using low-effective-mass conduction electrons in graphene, if successful, would allow for generation of far infrared (FIR) and terahertz (THz) radiation without requiring magnetic fields running into the tens of tesla. In order to investigate this possibility, we consider a situation in which electrons are effectively injected via pumping from the valence band to the conduction band using an IR laser source, subsequently gyrate in a magnetic field applied perpendicular to the plane of the graphene, and give rise to gain for an FIR/THz wave crossing the plane of the graphene. The treatment is classical, and includes on equal footing the electron interaction with the radiation field and the decay in electron energy due to collisional processes. Gain is found even though there is no inversion of the energy distribution function. Gain can occur for electron damping times as short as hundreds of femtoseconds.