Gaseous nitrogen detection using excited-state laser spectroscopy

Abstract

When light from a laser diode having a wavelength in the interval from 670 to 880 nm is directed through a sample containing nitrogen molecules, the nitrogen molecules do not absorb the laser light; but if the sample is energized under suitable conditions so that the nitrogen molecules are raised to the normally unpopulated ##EQU1## energy level, which differs in energy from a higher energy level .beta..sup.3 .pi.g by an energy difference corresponding to the wavelength of the laser light, then some of the laser light will be absorbed by driving the energized nitrogen molecules from the ##EQU2## energy level to the .beta..sup.3 .pi.g energy level. The amount of absorpiton is proportional to the concentration of nitrogen molecules in the sample. Thus, if the absorption by a sample having a known concentration of nitrogen molecules is determined, the unknown concentration of nitrogen molecules in a second sample can be determined by measuring the absorption in the second sample. The sample may be energized by a flashlamp, or by applying a strong electric field across the sample under suitable pressure conditions.