WATER-VAPOR SENSING USING POLARIZATION SELECTION OF A ZEEMAN-SPLIT ARGON DISCHARGE LAMP EMISSION-LINE

Water vapour concentrations are measured using the optical absorption of a Zeeman-split emission line of an argon discharge lamp. When a lon gitudinal magnetic field of the proper magnitude is used to split the emission line, two components of opposite circular polarization are pr oduced: one coincident, and one off-resonance with respect to a water vapour absorption line at 10 687.36 cm(-1). Differential absorption is directly measured by alternately selecting the polarization of the li ght which is allowed to propagate down the optical path into a multipa ss absorption cell. Water vapour concentration measurements were obtai ned over a range of over three orders of magnitude (similar to 0.002-3 .0%). The monitor was also shown to act directly as a mixing ratio (mo le fraction) sensor (within +/-10%) over a pressure range of 0.3-1.2 a tm.