Tunable diode laser based, one component instrument for open path measurements of trace concentrations of atmospheric gases

A simple tunable diode laser based system for routine monitoring of concentrations of atmospheric gases was developed. The instrument operation is based on a PbSnSe diode laser emitting radiation at about 4.7 microns, and InSb photodiodes. Usually, the laser operates in multimode regime with an optical power of about 0.1 mW in the mode. The system consists of the emitter-receiver unit (including optical elements and a cryostat with liquid nitrogen, which contains the diode laser and two InSb photodetectors) and the retroreflector. The instrument has two limitations: (1) the gas should have absorption lines within the mid-IR spectral region (4-8 microns) and (2) the gas should be stable enough while in the instrument's cell to allow periodic calibration of the instument. The instrument, which in the manufacturing stage, is presently used for carbon monoxide monitoring.