| Wavelength modulation absorption spectroscopy is a highly sensitive, non-intrusive technique for probing gaseous species, which employs the well-known principles of modulation spectroscopy in a novel way. With this technique, parameters such as velocity, density, and temperature can be measured with a high degree of precision. The research presented here shows that wavelength modulation is a convenient means of increasing the sensitivity of an absorption spectroscopy measurement because it allows for harmonic detection. The focus of the dissertation is resolution of overlapping spectra by harmonic detection and the advantages gained by performing detection at the higher harmonics, e.g., sixth and eighth.;Additionally, it is shown that the higher harmonic detection orders can be used to identify transition line shape profiles as well as absorption line parameters. A study of the line shape profile for the oxygen A-band transitions is presented. The results of this study indicate that oxygen exhibits collisional narrowing on the order of 0.006 cm-1 atm-1 in this near infrared atmospheric band. Other general characteristics of absorption signals obtained by employing wavelength modulation spectroscopy with harmonic detection are discussed along with their corresponding applications. |
