Off-axis cavity ringdown measurements of trace iodine

Off-axis cavity ringdown spectroscopy has been employed to measure trace levels of molecular iodine using continuum absorptions near 404 nm and 469 nm. Iodine concentrations ranging from 0 to 2 × 1012 molecules/cm3 were accurately measured to within ±4% and a measurement precision of 7.8 × 1011 molecules/(cm3 Hz1/2) in a 1 cm pathlength was empirically determined. The system, which does not require calibration and works in a variety of background gases, should find utility in quantifying residual iodine in oxygen–iodine chemical lasers and flow tube experiments.