Hydrogen and lithium Isotope analysis via optical spectroscopy of laser-produced plasmas

Abstract Accurate detection and quantification of light-element isotopes, particularly hydrogen (H) and lithium (Li), are essential across chemistry, materials science, geology, nuclear energy, forensics, and defense applications. Isotopic compositions provide insight into fuel cycles, materials degradation, mass transport, and environmental processes. Hydrogen and Li isotopes are especially relevant in nuclear environments because neutron induced reactions directly connect their isotopic inventories. Despite their importance, analysis of these light isotopes remains challenging due to their low atomic mass, high mobility, and, in some cases, radiological constraints. While some existing analytical techniques can detect and measure H and/or Li, they typically require sample preparation, laboratory-based instrumentation, or extended analysis times that preclude real-time monitoring capabilities. To address these limitations, optical spectroscopy of laser-produced plasmas offers a promising solution, enabling field-deployable, standoff sensing of isotopic signatures with real-time analysis capability and no sample preparation requirement. This Topical Review summarizes fundamentals and recent advances in H and Li isotopic analysis using optical spectroscopy, with emphasis on laser-produced plasmas generated by laser ablation of solid targets. Key concepts relevant to isotope-resolved optical measurements are introduced, including isotope shifts, fine and hyperfine structure, and line-broadening mechanisms. Progress in optical emission, laser induced fluorescence, and absorption spectroscopy is reviewed for H and Li isotopes 1 H, 2 H, 3 H, and 6 Li, 7 Li, respectively). The review concludes by identifying remaining challenges and opportunities for minimally destructive and field-deployable optical spectroscopy of light-element isotopes in complex environments.