Miniaturized Tunable Laser Spectrometer for the Simultaneous Detection of Water Ice and Hydrogen-Oxygen Isotopes for...

Distinguishing the origin of lunar water ice requires in situ isotopic measurements with high sensitivity and robustness under extreme lunar conditions; however, challenges such as uncertain water contents and isotopic fractionation induced by regolith particles restrict isotopic analysis. Herein, we present a miniaturized tunable diode laser absorption spectrometer (TDLAS) developed as the core prototype for the Chang'E-7 Lunar Soil Water Molecule Analyzer (LSWMA). The wavelength range of the instrument is 3659.5-3662.0 cm^-1, and the system integrates a Herriott cell for stable multi-isotope (H₂¹⁶O, H₂¹⁸O, H₂¹⁷O, and HD¹⁶O) detection and employs regolith samples of known isotopic experiments to quantify adsorption-induced fractionation. Performance evaluations demonstrated a dynamic water detection range of 0.01-2 wt % and isotope precision up to 1.3‰ for δD (30.5 s), 0.77‰ for δ¹⁸O (36 s), and 0.75‰ for δ¹⁷O (21.5 s) with extended averaging. Repeated injections of three types of standard water revealed a volume-dependent deviation (ΔδD up to -59.5‰) attributed to multilayer adsorption effects, while simulated lunar soil experiments identified additional isotopic fractionation (ΔδD up to -12.8‰) caused by particle binding. These results validate the ability of the spectrometer to resolve subtle isotopic shifts under lunar conditions, providing critical data for distinguishing water origins and advancing future resource utilization strategies.