Theory of the nitrogen laser excited by a relativistic electron beam

The 3371-Å nitrogen laser power produced by a relativistic electron beam propagating into nitrogen gas is calculated. The excitation contribution of cascade electrons is found to be negligible, compared to the excitation caused by plasma electrons drifting in the inductive electric field produced by the beam. The extensive experimental data on nitrogen are used wherever possible in the calculation, and the sensitivity of the calculation to the various input data is given. The mechanism of excitation by plasma electrons alone yields agreement within experimental uncertainty for such parameters as the peak laser power, the laser pulsewidth and delay, and the dependence of the laser power on gas pressure. For a larger drift tube radius, the plasma electron mechanism predicts higher power and a different pressure dependence, in agreement with experimental trends. In calculating the laser power, the beam propagation details, excitation to the upper and lower laser levels, collisional quenching, a threshold for amplified spontaneous emission, and excitation and deexcitation by plasma electrons are included, but coherent dipole moment effects are neglected.