By Cnr Ifn
Cavity-ring-down-spectroscopy is a traditional linear spectroscopy approach where the intra-cavity absorption of a gaseous species is extracted from the measurement of the cavity photon lifetime. After a first demonstration, a few years ago, of a near-infrared apparatus operated in a frequency-agile rapid-scanning (FARS) scheme, we are now working at its extension to the mid-infrared by exploiting a difference-frequency-generation process. This involves the nonlinear interaction between a powerful 1064-nm pump laser and an electro-optically tunable signal laser in the telecom region. An optical frequency comb ensures frequency calibration to the pump and signal lasers and thus to the nonlinearly generated mid-infrared beam coupled into the high-finesse optical cavity. The system is planned to be applied to the investigation of several lines od the D 2 and HD hydrogen isotopologues that lie in the 3-3.5 µm region.
