Development of a jet-REMPI (resonantly enhanced multiphoton ionization) continuous monitor for environmental applications

The need for a continuous monitor for environmentally important pollutants at realistic [parts-pertrillion (parts in 10(12))] concentrations measured in real time (minutes) is widely recognized. We developed an instrument tha t is based on supersonic-jet expansion and cooling, followed by resonantly enhanced multiphoton ionization (REMPI) into a mass spectrometer. This appr oach furnishes the dual selectivity of narrow-band tuned laser absorption a nd mass analysis. We initiated a spectroscopic characterization of the jet' s collisional cooling behavior to optimize the instrument's sensitivity and selectivity, made measurements of several aromatic compounds (including po lychlorinated dioxins) by use of a one-color REMPI scheme, and demonstrated a two-color excitation scheme. (C) 2001 Optical Society of America OCIS co des: 010.1120, 120.1740.