The present invention relates to detection of subsoil contaminants including chlorinated hydrocarbons. More specifically, but without limitation thereto, the present invention relates to a fiber optic probe for detecting Raman emissions that may be used with a cone penetrometer.
Raman spectroscopy is an emission technique that uses scattering of incident optical energy to produce spectral peaks that are frequency shifted from the incident optical energy. These so-called Raman emissions are believed to arise from changes in molecule polarization. Virtually all organic molecules display a characteristic Raman emission. The inherently high resolution of Raman spectra often permits the analysis of several chemicals present together in a mixture. This technique is particularly applicable to detecting chlorinated hydrocarbons that frequently contaminate subsoil around aquafers. Cone penetrometers have been used with a variety of probe designs to detect these contaminants.
The advent of inexpensive, portable Raman spectrometers has gained renewed interest in the area of Raman spectrometry. These spectrometers offer a minimum of components compared to conventional instrumentation and provide high light throughputs.
Despite the advantages of Raman spectroscopy and the technological advances, there are additional issues that must be resolved to realize a practical fiber optic Raman sensor (FORS), such as low sensitivity and interference from Raman emissions in the optical fibers.
A need therefore exists for a fiber optic Raman sensor that suppresses interference from the optical fibers, is operable with optical fiber lengths in excess of 30 meters, has high sensitivity, and is rugged enough to be deployed in a cone penetrometer.