Quantum theory of incoherent THz emission of an interacting electron-ion plasma

The THz spectrum of the spontaneous emission of an interacting electron-ion gas, recently observed in laser pulse ionized air, is theoretically analyzed. Using the correlation expansion of the involved many particle system, the contribution of electron-molecule and electron-ion collisions to the transitions in the free electron continuum are treated. Depending on the particle density and the ion distribution, electromagnetic emission is found from the terahertz range up to optical frequencies.