Gaseous nitrogen detection using excited-state laser spectroscopy

A method for measuring the concentration of nitrogen molecules in a sample, comprising the steps of:

• (a) introducing into a sample chamber a first sample of gas having a known concentration of nitrogen molecules;
• (b) periodically directing a beam of photons having a wavelength between 670 and 880 nm through the sample chamber;
• (c) measuring the intensity N.sub.0 of the beam after it has passed through the sample chamber containing the first sample;
• (d) energizing the sample sufficiently to raise the nitrogen molecules to the normally unpopulated ##EQU27## energy level, which differs in energy from a higher energy level B.sup.3 .pi.g by an energy difference corresponding to a photon wavelength of between 670 and 880 nm;
• (e) periodically directing a beam of photons having a wavelength between 670 and 880 nm through the energized first sample;
• (f) measuring the intensity N.sub.E of the beam after it has passed through the sample chamber including the energized sample;
• (g) determining the reduction in intensity N.sub.0 -N.sub.E that results from energizing the sample;
• (h) replacing the first sample of known concentration by a second sample having an unknown concentration of nitrogen molecules;
• (i) periodically directing a beam of photons having a wavelength between 670 and 880 nm through the sample chamber;
• (j) measuring the intensity X.sub.0 of the beam of photons after it has passed through the sample chamber containing the second sample;
• (k) energizing the second sample in such a way that the nitrogen molecules in it are raised to the normally unpopulated ##EQU28## energy level, which differs in energy from a higher energy level B.sup.3 .pi.g by an energy difference corresponding to a photon wavelength of between 670 and 880 nm;
• (l) periodically directing a beam of photons having a wavelength between 670 and 880 nm through the energized second sample;
• (m) measuring the intensity X.sub.E of the beam that has passed through the sample chamber including the energized second sample;
• (n) determining the reduction in intensity X.sub.0 -X.sub.E associated with energizing the second sample;
• (o) calculating the concentration of nitrogen molecules in the second sample by the equation ##EQU29##

Apparatus for use in determining the concentration of nitrogen molecules in a sample of unknown concentration from the known concentration of a calibration sample of the same thickness and at the same pressure, comprising in combination:

• a sample chamber;
• first means located adjacent said sample chamber for successively energizing samples of known and of unknown concentration so that the nitrogen molecules in the samples are in the excited ##EQU30## state when the sample is energized;
• second means located adjacent said sample chamber for successively measuring the absorption of light having a wavelength less than 880 nm by the excited samples of known and of unknown concentration;
• third means electrically connected to said second means for determining the concentration of nitrogen molecules in the sample of unknown concentration from the absorption measured by said second means and from the known concentration of the calibration sample.