We have examined the utility of a gas-filled, Nd:YAG-laser-pumped Raman shifter as a possible broad-spectrum light source. Six to nine new output frequencies with pulse energies above 1 µJ are produced when a pure-hydrogen or pure-methane Raman shifter is pumped with 40 mJ of secondharmonic, 20 mJ of third-harmonic, or 11 mJ of fourth-harmonic pump pulse energy. Optimum output occurs at pressures of approximately 10 atm for the pure-gas experiments. We also report the output frequencies and pulse energies of a mixed hydrogen-methane Raman shifter pumped by 20 mJ of the third harmonic of the laser for various proportions of the two gases at pressures up to nearly 20 atm. Depending on composition and pressure, over a dozen new output lines with pulse energies over 1 µJ can be produced. We discuss the nonlinear processes involved, the optimum operating conditions, and the suitability of the source for our application of groundwater monitoring.

Direct, in situ monitoring of many groundwater contaminants is possible using the Remote Laser-Induced Fluorescence (RLIF) technique.We have designed, laboratory-tested, and field-tested a prototype mobile instrument capable of performing such monitoring. It consists of a portable, computer-controlled fluorimeter with a frequency-quadrupled Nd:YAG laser as a UV excitation source, detachable fiber optic sensor, and a detection module employing two photomultiplier tubes and a dualchannel boxcar averager for signal recovery. In this report, we give a complete description of the hardware and software utilized in the instrument, along with a summary of our field testing procedures and experiences, and an assessment of the technique's current and potential capabilities. 423 Copyright© 1987 by Marcel Dekker, Inc. Downloaded by [McMaster University] at 00:02 16 June 2016 424 KENNY ET AL.

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