Nonlinear Raman spectroscopies with Raman shifter for sensitive gas detection

In recent years, measurements of the trace greenhouse gases such as CO/sub 2/, and CH/sub 4/ has become important due to environment problems. In chemical plants and gas pipe lines, continuous monitoring of the leak of inflammable gases is also very important from the safety point of view. We proposed a new scheme for nonlinear Raman spectroscopy, in which a fixed-frequency laser is combined with a Raman shifter. In the scheme, no IR tunable laser is required like absorption spectroscopy and photo-acoustic spectroscopy (PAS). We applied this scheme to different kinds of nonlinear Raman spectroscopy; photo-acoustic Raman spectroscopy (PARS), coherent anti-Stokes Raman spectroscopy (CARS) and stimulated Raman gain spectroscopy (SRGS).