HIGH-SENSITIVITY DETECTION OF MOLECULAR ABSORPTIONS BY SEMICONDUCTOR DIODE-LASERS AT WAVELENGTH LOWER THAN 2 MU-M

We present some recent measurements performed on absorption overtone transitions of molecular species, interesting for environmental and spectroscopic applications, by means of semiconductor diode laser at wavelengths lower than 2 mu m. The characteristics of the semiconductor diode lasers needed for this application are described. Different detection techniques have been compared testing the sensitivity of the apparatus by means of absorption detection of Methane at 886 nm. A spectroscopic characterization of Ammonia at 1.65 mu m and Acetylene at 789 nm have been performed by studying the pressure broadening behaviour at different temperatures. Sensitivity measurements of these molecules at atmospheric conditions have been done in order to know the minimum detectable concentration of the system. The measured values were 0.08 ppm/Km for NH3 in N-2 and 0.2 ppm/Km for C2H2 in air.