Measuring variations of 18O and 2H in atmospheric water vapour using laser spectroscopy: an instrument characterisation study Variations of stable water isotopes in water vapour have become measurable at a measurement frequency of about 1 Hz in recent years using novel laser spectroscopic techniques. Picarro L2140-i超高精度液態(tài)水/水汽同位素分析儀 Picarro L2130-i超高精度液態(tài)水/水汽同位素分析儀