A Broadband and Compact Dual Comb Spectrometer for Precise Field Detection of Trace Elements and Chemicals

There is a growing need to accurately characterize nuclear materials not only for nuclear safeguards and nonproliferation treaty verification but also for forensics and provenance. At present, nuclear material identification requires samples to be collected and sent to laboratories for analysis using large and expensive equipment, such as inductively coupled plasma mass spectrometers (ICP-MS) or secondary-ion mass spectrometers (SIMS). This can take weeks, if not months, to obtain results, and utmost care must be taken to ensure the integrity of the sample. Optical techniques, such as laser-induced breakdown spectroscopy (LIBS) and tunable diode laser absorption (TDLAS), show potential as a viable field detector for nuclear materials. However, field LIBS instruments suffer from poor spectral resolution to detect isotopic shifts of nuclear materials while TDLAS instruments lack broad spectral coverage for multi-species detection.  To overcome these limitations, we propose a laser-ablation dual comb spectrometer (LA-DCS) that can provide both broad spectral coverage and high spectral resolution in a compact form factor. Feasibility was demonstrated by characterizing the analytical performance of the measurement using surrogate materials in Phase I, along with specifically looking at the engineering requirements to reduce the size, weight and power (SWaP) of the current Er-fiber DCS into a portable system. We have shown that we could identify the ground state hyperfine splittings in rubidium, a nuclear material surrogate, following a single laser shot. Multiple species identification can be performed with this technology, making it highly suitable for particulate analysis in nuclear forensics.