New Laser Spectroscopy Technique Promises Breakthrough in Fusion Fuel Monitoring

A recent study conducted by researchers from the Korea Institute of Fusion Energy and Jeonbuk National University presented a novel technique for analyzing lithium isotopes in liquid samples. This study, led by Duksun Han of the Korea Institute of Fusion Energy, proposed a new method that integrated two laser-based techniques: laser-produced vaporization (LPV) and laser-induced breakdown spectroscopy (LIBS) (1). Han and his team demonstrate how LPV-LIBS can analyze lithium isotopes in liquid samples, which is important in achieving tritium self-sufficiency in future fusion reactors (1). The study’s findings were published in the Spectrochimica Acta Part B: Atomic Spectroscopy (1).

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Fusion energy is a form of nuclear power that helps generate electricity and heat (2). It has long been hailed as the panacea to solve the issue of sustainable power, relying on a fuel cycle involving deuterium and tritium (²H and ³H) (3). In this cycle, lithium-6 (⁶Li) plays a key role by reacting with neutrons to produce tritium, making its availability and precise measurement essential for the success and safety of fusion reactors (1). Because of this reason, ⁶Li enrichment is in high demand.

To meet the rising demand for high ⁶Li enrichment and facilitate accurate isotopic monitoring, Han’s team developed the LPV-LIBS method, which was designed to play into the strengths of both techniques. LPV vaporizes liquid lithium chloride (LiCl) samples using a high-powered pulsed laser, while LIBS analyzes the resulting plasma through optical emission spectroscopy (1).

For their method, the researchers used a nanosecond Nd:YAG laser equipped with dual outputs—one beam at 532 nm for vaporization, and another at 1064 nm for plasma generation. Rather than ablating the liquid directly, which often yields weak signals and inconsistent results, the 532 nm beam created a vapor cloud above the sample (1). Then, the second beam targets this vapor to induce plasma suitable for spectroscopy.

By analyzing the 2s–2p transition line in lithium’s emission spectrum, researchers were able to distinguish between ⁶Li and ⁷Li isotopes with high accuracy (1). The spectral shift between the two isotopes was measured at 15.7 picometers (1). Furthermore, the optimal pulse energies for both lasers were determined to maximize signal intensity while avoiding the "self-reversal" effect—a distortion in spectral readings caused by excessive energy input.

The results of the study showcase the potential of the LPV-LIBS method. In particular, the researchers highlighted the measurable increase in lithium vapor production, which directly correlated with the spectral intensity (1). The minimum pulse energy required to generate plasma in the vapor was 3 mJ, while 30 mJ was sufficient to initiate vaporization (1).

The isotope ratio analysis yielded a correlation coefficient (R²) of 0.998, indicating a high degree of accuracy (1). The standard error for the method ranged from 2.5% to 5.2%, making it competitive with, and in some cases superior to, existing isotope analysis technologies that often require more elaborate instrumentation and sample preparation (1).

As a result, LPV-LIBS is demonstrated in this study to be operable under atmospheric pressure. Because of this, LPV-LIBS can be used to simplify lithium isotope analysis. Han and his colleagues emphasized in their study that the technique can not only be valuable in fusion energy development, but that LPV-LIBS can also be broadly applied to other functions in the nuclear energy industry where rapid, precise isotope monitoring is critical (1).

Currently, the ongoing trade war is intensifying, and it is impacting fusion power efforts (3). As countries around the globe look for ways to remain competitive in this field, it is expected that new techniques such as LPV-LIBS will emerge to overcome the current technical hurdles. By streamlining isotope analysis, the method enhances our ability to monitor and optimize fuel cycles (1).

References

1. Tran, T. N.; Han, D.; Shim, S.; Choi, D. H. Isotopic Analysis of Liquid Lithium via Laser-produced Vapor for Laser-induced Breakdown Spectroscopy. Spectrochimica Acta Part B: At. Spectrosc. 2025, 225, 107121. DOI: 10.1016/j.sab.2025.107121
2. U.S. Department of Energy, Nuclear. Energy.gov. Available at: https://www.energy.gov/nuclear#:~:text=Nuclear%20power%2C%20the%20use%20of,to%20support%20national%20defense%20activities. (accessed 2024-04-17).
3. Pao, J. Trade War Jeopardizes China’s Fusion Energy Drive. Asia Times. Available at: https://asiatimes.com/2025/04/trade-war-jeopardizes-chinas-fusion-energy-drive/# (accessed 2025-04-17).