Quantitative gas sensing by backscatter-absorption measurements of a pseudorandom code modulated λ∼8-μm quantum cascade laser

We have demonstrated quantitative chemical vapor detection with a multimode quantum cascade (QC) laser. Experiments incorporated pseudorandom code (PRC) modulation of the laser intensity to permit sensitive absorption measurements of isopropanol vapor at 8.0 pm. The demonstration shows the practicality of one technical approach for implementing low-peak-power QC lasers in the transmitter portion of a differential absorption lidar (DIAL) system. With a 31-chip, 300-ns/chip PRC sequence, the measured isopropanol detection limit was 12 parts in 10(6) by volume times meters (similar to 3 X 10(-3) absorption) for a simple backscatter-absorption measurement configuration. (C) 2000 Optical Society of America OCIS codes: 280.1910, 140.3070.