Diode laser spectroscopy of ammonia at 760 nm

Abstract A tunable diode laser spectrometer has been employed to examine the unknown overtone absorption lines of NH 3 around 13 , 100 cm - 1 (760 nm). The spectrometer sources are commercially available heterostructure AlGaAs tunable diode lasers operating in the “free-running” mode. The detection of the lines has been possible by the use of the wavelength modulation spectroscopy and the second harmonic detection technique. A special algorithm has been used in order to fit the highly modulated absorption lines. The weakest observed resonances have absorption cross sections on the order of ≃ 1 × 10 - 25 cm 2 /molecule or ≃ 0.3 km - 1 /amagat. For some of the more intense lines self-, air-, N 2 -, He- and H 2 -broadening coefficients have been obtained at room temperature and also some shifting coefficients have been measured.