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. Presently, 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 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 viable field detectors for nuclear materials. However, field LIBS instruments suffer from poor spectral resolution to detect isotopic shifts of nuclear materials while TDLAS lack broad spectral coverage for multi-species detection. To overcome these limitations, we propose a fiber-based dual comb spectrometer (DCS) that provides both broad spectral coverage and high spectral resolution in a compact form factor. In recent work we have demonstrated the feasibility of this DFC approach by identifying and resolving isotopic and ground state hyperfine splittings in rubidium following a single laser ablation shot, as well as identification of multiple species simultaneously utilizing the inherently broad optical bandwidth of the DCS. In this Phase I effort, we will demonstrate the feasibility of fiber-based DFC as a compact field analyzer of trace elements capable of high resolving power to isotopes shifts and their ratio of nuclear surrogate materials over a broad spectral range. This will lead to the miniaturization of the instrument in Phase II.