High Precision Broadband Optical Spectrometer for Nuclear Forensics

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 lab-based high precision broadband dual comb spectrometer (DCS) can detect multi-element and multi-isotope detection and characterization of materials for nuclear forensics. 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 a broadband titanium:sapphire femtosecond DFC as a novel spectrometer operating at high repetition rates to enable fast analysis of materials containing trace elements and their isotopes for nuclear forensic applications. This will lead to the development of a prototype instrument in Phase II. The proposed technology using a broadband dual frequency comb source for high precision absorption spectroscopy can be used to identify, characterize and analyze various materials for elemental composition and isotopic analysis in real-time. Our technology will also be much more compact than mass spectrometer, allowing our technology to be more suitable for field applications and in challenging environments. The proposed technology will also benefit the analytical chemistry community and pharmaceutical industry where the spectrometer can be applied to high precision spectroscopy to identify various chemical compounds.