Laser-Induced Fluorescence from N sub(2) super(+) Ions Generated by a Corona Discharge in Ambient Air

In this work, we present the measurement of laser-induced fluorescence from N sub(2) super(+) ions via the band system in the near-ultraviolet. The ions were generated continuously by a plasma glow discharge in low pressure N sub(2) and by a corona discharge in ambient air. The fluorescence decay time was found to rapidly decrease with increasing pressure leading to an extrapolated decay rate of approximately 10 super(10) s super(-1) at atmospheric pressure. In spite of this quenching, we were able to observe laser induced fluorescence in ambient air by means of a time-gated spectral measurement. In the process of comparing the emission signal with that of N sub(2) spontaneous Raman scattering, ion concentrations in ambient air of order 10 super(8-)10 super(10) cm super(-3) were determined. With moderate increases in laser power and collection efficiency, ion concentrations of less than 10 super(6) cm super(-3) may be measurable, potentially enabling applications in atmospheric standoff detection of ionizing radiation from hazardous radioactive sources.