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 t ransitions of molecular species, interesting for environmental and spe ctroscopic applications, by means of semiconductor diode laser at wave lengths lower than 2 mu m. The characteristics of the semiconductor di ode lasers needed for this application are described. Different detect ion techniques have been compared testing the sensitivity of the appar atus by means of absorption detection of Methane at 886 nm. A spectros copic 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 de tectable concentration of the system. The measured values were 0.08 pp m/Km for NH3 in N-2 and 0.2 ppm/Km for C2H2 in air.