Long-path absorption measurement of CO2 with a Raman-shifted tunable dye laser

A laser long-path absorption system was developed with a hydrogen Raman shifter pumped by a tunable dye laser. The absorption spectrum of CO2 in the 2-micrometer region was measured in the open air with a retroreflector or a hard target. The concentration of CO2 was determined from the spectrum by the least-squares method. Noise in the system was analyzed, and the propagation of error to the obtained concentration was investigated. The statistical error in the concentration was estimated at approximately 1% for a single spectrum measurement. Comparison with the simultaneous measurements with a nondispersive infrared gas analyzer showed good agreement.