Trace detection of hydrazines by optical homodyne interferometry

A photothermal laser interferometric system is described that has sufficient sensitivity to allow the detection of the hydrazines: hydrazine, monomethylhydrazine, and unsymmetrical dimethyihydrazine at part per billion concentrations. A line tunable CO(2) laser excites the trace hydrazine molecules in one arm of a modified Jamin interferometer illuminated with a single frequency He-Ne laser. The CO(2) laser beam intersects one of the He-Ne beams in the interferometer at a small angle, so there is no interaction of the IR and visible laser beams at any optical components in the system. The system operates with computer control of interferometer alignment, CO(2) excitation laser tuning, and data acquisition.