Diode laser molecular spectroscopy
This experiment concerns the Molecular Spectroscopy of molecules of atmospheric interest, like CH4, CH3Cl, CH3F, CH3I, C2H2, C2H4, CO2, H2O, NH3, O2.
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-1 (3σ) and its sensitivity permits the detection of absorption lines with intensity (S) around 10-26 cm/molecule, with extinction coefficients of the order of magnitude of tens of km·amagat.
A particular of the laser diode beam reflections on one of the two mirrors of the multipass Herriott type measurement cell as seen by an infrared camera.
Carbon dioxide transmission spectrum around 7820 Å (R branch turning point) with the relative rotational quantum numbers, obtained by WMS and the the 2nd harmonic detection, at room temperature, pCO2 = 91 Torr, and 10 Hz bandwidth.
Personale INO dipendente:
Lucchesini Alessandro, Gozzini Silvia, Tagliaferri Mauro,