Diode laser molecular spectroscopy
This experiment concerns the Molecular Spectroscopy of molecules of atmospheric interest, like CH<sub>4</sub>, CH<sub>3</sub>Cl, CH<sub>3</sub>F, CH<sub>3</sub>I, C<sub>2</sub>H<sub>2</sub>, C<sub>2</sub>H<sub>4</sub>, CO<sub>2</sub>, H<sub>2</sub>O, NH<sub>3</sub>, O<sub>2</sub>.
By using monomodal semiconductor lasers as the sources, noise reduction techniques, such like the Wavelength Modulation Spectroscopy (WMS) along with the phase detection, and the aid of multipass measurement cells, remarkable results have been obtained in the characterization of overtone resonances of such molecules in VIS and NIR part of the e.m. spectrum.
In fact, working with the laser diodes in “free-running” or in “extended cavity” modes and sweeping them in frequency, specific ro-vibrational molecular parameters can be measured with high precision for each studied molecule.
The maximum resolution attainable by this spectroscope is on the order of 0.01 cm<sup>-1</sup> (3σ) and its sensitivity permits the detection of absorption lines with intensity (S) around 10<sup>-26</sup> cm/molecule, with extinction coefficients of the order of magnitude of tens of km·amagat.