Isotopic trace analysis of water vapor with multipass cavity Raman scattering.

Cavity-enhanced spontaneous Raman scattering was investigated as a means of simple and inexpensive isotopic water analysis. A multimode blue laser diode equipped with a feedback-generating multipass cavity provided a 100-fold Raman enhancement at a pump linewidth of 3.5 cm-1. Samples containing trace amounts of 1H2H16O were probed at deuterium-hydrogen concentration ratios ranging from 157 parts-per-million (local seawater) down to 8 parts-per-million (deuterium depleted water). All measurements were performed in argon or dried air at atmospheric pressure at 1H2H16O concentrations nearing 100 parts per billion with an uncooled camera at exposure times as short as a few minutes.