Gain and saturation of the nitrogen ion laser

Abstract

In this work a dilute nitrogen plasma pumped by charge transfer from He+2 has been operated as a pulsed optical amplifier. In the experimental system used two synchronously excited plasmas were produced by preionized discharges in an atmospheric electrical avalanche device switched by hydrogen thyratrons so that repetitive operation to 30 Hz would be possible. The plasmas were electrically connected in a transverse series circuit to provide a phase delay in their excitation comparable to the optical transit time between them. Laser output at 427.8 nm from the first discharge coupled to the fields in a self-excited oscillator geometry was threaded through the second along its 85-cm longer dimension. Calibrated attenuation of the beam from the oscillator subsequently input to the amplifier provided data on the overall amplification ratio to which the two adjustable parameters of a simple model were fit. From these parameters overall small-signal gains as large as 2×106 were found together with saturation intensities of the order of 50 kW/cm2. Under the same conditions a gain of about 18 was found at an output intensity of 1 MW/cm2, conditions relatively near the ideal extraction of power at zero gain.