WAVELENGTH-MODULATION DETECTION OF ACETYLENE WITH A NEAR-INFRARED EXTERNAL-CAVITY DIODE-LASER

An external-cavity diode laser operating at 1500 nm was used to record the combination band of acetylene (C2H2). By combination of wavelengt h-modulation spectroscopy with a noise-canceler detection circuit, a m inimum detectable absorbance of 4.8 x 10(-4) with a 300-ms time consta nt was achieved, although this result was limited by etalon fringes. W hen combined with this detection technique, continuous, widely tunable output from an external-cavity laser is ideally suited for high-resol ution absorption spectroscopy with excellent sensitivity. (C) 1995 Opt ical Society of America