SENSITIVE DETECTION OF AMMONIA ABSORPTION BY USING A 1.65 MU-M DISTRIBUTED-FEEDBACK INGAASP DIODE-LASER

We have developed a 1.65 mu m DFB diode laser absorption spectrometer to allow high sensitive detection of ammonia at this wavelength. The study was done over 1.66454 mu m (6007.6cm(-1)) component of v(2) + v(3) + v(4) re-vibrational combination band of NH,. An apparatus sensitivity limit of 2ppm-m of pure NH3 was measured by using a phase-sensitive low-wavelength-modulation (LWM) detection technique. Minimum detectable concentrations of 55 ppm-m of NH3 in N-2, and 59 ppm-m of NH3 in O-2 at a total pressure of 76 Torr and a temperature of 295 K were measured. Also, we have measured the unknown selfbroadening and foreign gas broadening coefficients for N-2 and O-2 for this line and their gas temperature dependence.