Optical fiber laser Raman sensor for monitoring hydrocarbons

An all-optical sensor for monitoring the concentration ratio of ethanol and methanol in mixture samples of water/gasoline was devised on the basis of spectrum analysis of the various sample compositions. A fiber optic Raman sensor was developed as a probe indicator for component detection of such hydrocarbon mixtures. The sensor employs a frequency-doubled 532 nm continuous wavelength (CW) Nd:YAG laser and a specially designed fiber optic Raman probe. The attractiveness of this scheme lies in online determination of sample constituents (1) without changing to a specially designed infrared (IR) fiber with complicated and expensive IR spectroscopy and, (2) with no change in sample physical or chemical properties. Spectral analysis techniques based on spectral shape band intensities and areas and some multi-component analysis are tested to find the most effective tool for measuring ethanol and methanol in a mixture. This work demonstrates that this sensor is capable of monitoring methanol and ethanol in water and gasoline solution.