The nitrogen ion laser pumped by charge transfer

Charge transfer from He+
2
to N
2
has been used in a variety of devices to pump significant levels of inversion of the
B^{2}\Sigma_{u}
electronic transistion of N+
2
. Laser output has been achieved at three wavelengths, 391.4, 427.8, and 470.9 nm. Each has corresponded to a transition from the same upper laser level to lower levels having vibrational quantum numbers equal to 0, 1, and 2, respectively. With proper mirror sets each has been individually excited. Studies of the scaling and efficiency at which the laser output could be obtained have been made with devices pumped by
e
-beams, preionized avalanche discharges, and preionized resonant and traveling wave discharges. The possible efficiencies for the extraction of the energies stored in the inversions have been examined for various configurations of the coupling of the optical fields to the plasmas. Resulting devices have included self-excited oscillators, regenerative amplifiers, and master oscillator power amplifiers. The experimental results have supported a kinetic model which generally explains the unique features of the nitrogen ion laser. Of particular interest is the capacity of these systems to support the simultaneous optimization of both scale and efficiency. With
e
-beam excitation optical power densities of 320 MW . l
^-1
have been achieved at a constant power transfer efficiency of 3 percent. With resonant discharge excitation 44 MW . l
^-1
have been demonstrated at power conversion efficiencies of 2 percent and overall efficiencies ranging from 0.2 to 0.4 percent. From these results the kinetic model has projected an overall efficiency of 0.9 percent to be ultimately realized in a discharge device.