LONG-DISTANCE SIMULTANEOUS DETECTION OF METHANE AND ACETYLENE BY USING DIODE-LASERS COUPLED WITH OPTICAL FIBERS

Remote simultaneous detection of methane and acetylene by using two single-mode diode lasers emitting at 1.66 and 1.53-mu-m, respectively, coupled with 4-km optical fibers has been demonstrated by laboratory simulations. The lasers were modulated at different frequencies to measure in real-time the absorption of the two chemical species without interference. The gases could be detected quantitatively by the ratio of the phase-sensitive-detected fundamental and second-harmonic signals. When the absorption pathlength was 10 cm, the minimum detectable concentrations of methane and acetylene in air were 5 and 3 ppm, respectively, for a signal averaging time of 1 s.