LASER-BASED FLUORESCENCE EEM INSTRUMENT FOR IN-SITU GROUNDWATER MONITORING

A fluorescence excitation-emission matrix (EEM) instrument is describe d which employs laser excitation and optical fiber light delivery for remote sensing applications. Ultraviolet laser light is generated at a variety of discrete wavelengths by pumping a Raman shifter with the t hird or fourth harmonic of a Nd:YAG laser, and this Raman-shifted ligh t is used for fluorescence excitation to generate EEM spectra. Seven-m eter optical fibers are used for laser beam delivery and fluorescence light collection, and a diode array detector is used to detect fluores cence emission spectra. As a test of the capability of this instrument , the composition of a two-component mixture of the groundwater pollut ants carbazole and p-cresol is determined quantitatively by least-squa res analysis of the mixture's fluorescence EEM. Detection limits were in the ppb range and the linear dynamic range was better than 3 orders of magnitude.