Measurements of the isotopic composition of water vapor using a DFGbased spectrometer at 2.8(mu)m

We report on absorption measurements of the isotopic composition of water in a demineralized sample by means of wavelength modulation spectroscopy of H2O lines in the spectral region around 2.8(mu)m. The mid-IR radiation was obtained by difference-frequency mixing of the radiation of an extended cavity diode laser ((lambda)=780nm) and that of a diode-pumped monolithic Nd–YAG laser. Preliminary tests indicate the possibility of obtaining a precision for the 18O/16O, 17O/16O and 2H/16O isotope ratio measurements of the order of 1 per mil.