Isotopic trace analysis of water vapor with multipass cavity Raman scattering

Abstract

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.