Signatures of rare-earth elements in mineralogical form using laser-ablation dual-comb spectroscopy

Andrew Jarymowycz; Arthur K. Mills; Avery Wong; Christina Hofer; David J. Jones; Dylan Tooley; Errol Bowman; Hope Dannar; Ian Pang; John J. McCauley

arxiv: 2605.03157 · v1 · submitted 2026-05-04 · ⚛️ physics.optics · physics.atom-ph· physics.plasm-ph

Signatures of rare-earth elements in mineralogical form using laser-ablation dual-comb spectroscopy

Christina Hofer , Errol Bowman , Andrew Jarymowycz , John J. McCauley , Dylan Tooley , Hope Dannar , Avery Wong , Ian Pang

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Arthur K. Mills Mark Phillips R. Jason Jones David J. Jones

This is my paper

Pith reviewed 2026-05-07 02:26 UTC · model grok-4.3

classification ⚛️ physics.optics physics.atom-phphysics.plasm-ph

keywords elementssamplesspectroscopylinesmatrixmineralogicalmolecularrare-earth

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The pith

Dual-comb absorption spectroscopy resolves atomic, ionic, and molecular REE lines in mineral samples with sub-GHz resolution across THz bandwidths, yielding preliminary detection limits of 54-583 ppm and faster temporal dynamics than in metal alloys due to matrix effects.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The work tests a laser-based absorption technique called dual-comb spectroscopy on rocks and alloys containing rare-earth elements. Two frequency combs create a broad light spectrum that passes through a laser-produced plasma from the sample. This records thousands of narrow absorption lines at once, showing which elements are present. The method distinguishes individual rare-earth lines from other elements in the rock matrix better than standard spark-based techniques. Tests on certified rock powders and a lab-made copper alloy showed lines from lanthanum, samarium, and cerium appearing and fading at different times. The rock samples produced shorter-lived signals, likely because oxygen in the minerals encourages molecule formation. Early estimates suggest the approach can detect these elements down to a few hundred parts per million. The authors position it as a complementary tool to existing laser breakdown methods for field mineral mapping.

Core claim

Dual-comb absorption spectroscopy resolves individual REE and matrix lines with minimal spectral overlap and provides preliminary limits of detection from 54-583 ppm for La I, Sm I and Ce I in CRMs using univariate analysis.

Load-bearing premise

That the selected absorption transitions remain free of significant matrix-element overlap and that univariate peak analysis yields reliable concentration estimates without multivariate calibration or full plasma modeling.

read the original abstract

Spectroscopy of laser-produced plasmas offers an avenue for real-time, standoff and non-preparatory sensing of rare-earth elements (REEs) within a mineralogical context with applications spanning exploration geology to ore body mapping to ore sorting. Demonstrations of laser-induced breakdown spectroscopy (LIBS) in rock samples have employed both atomic and molecular detection for REE sensors. In this work we evaluate a complementary technique of absorption spectroscopy, realized with dual-frequency combs. This approach provides multi-THz (nm) spectral coverage with simultaneous sub-GHz (pm) resolution. It can improve accuracy and line identification confidence in congested multi-species spectra, which makes it ideal for multi-species evaluations present within mineralogical samples. We analyze REE signatures in calibrated reference materials (CRMs) and a synthesized, REE-containing alloy for atomic, ionic and molecular (oxide) absorptions across three spectral windows. We identify lines from rare-earth and matrix elements, compare absorption line strengths and investigate their temporal evolution. For La I, Sm I and Ce I, preliminary limits of detection from 54-583 ppm are estimated for CRMs, using univariate analysis of selected transitions. Comparing the CRM signatures to those of REEs synthesized in a copper alloy, we observe that most all REE lines appear earlier and disappear faster in the CRM samples. We attribute these dynamics to matrix effects: Among other elements, the increased oxygen content in the CRM could favor molecular formation. For rock samples, observations will once again differ due to grain sizes and bonding mechanisms. Compared to LIBS, we can resolve individual REE and matrix lines with minimal spectral overlap. These proof-of-principle results form a foundation for further development of this laser-based method as a mining sensor.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

Dual-comb absorption on laser-ablated minerals gives cleaner REE line resolution than typical LIBS but the abstract supplies no spectra, calibration curves, or quantitative matrix modeling, so the LOD claims and temporal interpretations stay unverified.

read the letter

The main thing here is a first reported combination of dual-comb absorption spectroscopy with laser ablation of rare-earth-bearing minerals and CRMs. They scan three windows, pick out La I, Sm I, Ce I and some matrix lines, note that most REE features appear and decay faster in the oxide-rich CRMs than in a copper alloy, and quote univariate LODs between 54 and 583 ppm. That temporal contrast and the claim of minimal overlap are the concrete observations on offer. The resolution advantage over LIBS is real in principle because dual-comb gives simultaneous broad coverage at sub-GHz linewidths, which helps in crowded spectra. The authors are also straightforward that grain size and bonding in actual rock will change the picture again. Beyond that the paper is thin. No raw spectra, no line lists with assignments, no error bars on the LODs, and no attempt to model the plasma chemistry that would explain why the CRM signals vanish faster. The matrix-effect discussion is therefore still qualitative. Because only the abstract is available, it is impossible to check whether the chosen transitions really sit clear of overlaps or whether baseline subtraction is stable enough for the quoted detection limits. This is the sort of incremental applied-spectroscopy note that could interest mining-sensor groups once the supporting data and a short plasma-dynamics section are added. It does not yet contain enough to shift practice or to serve as a methods reference. I would send it to review only if the full manuscript includes the missing spectra and at least a basic check on matrix interferences; otherwise it is still too early.

Referee Report

2 major / 2 minor

Summary. The manuscript evaluates dual-comb absorption spectroscopy of laser-produced plasmas as a complementary technique to LIBS for standoff detection of rare-earth elements (REEs) in mineralogical samples. Using calibrated reference materials (CRMs) and a synthesized REE-containing copper alloy, the authors identify atomic (La I, Sm I, Ce I), ionic, and molecular (oxide) absorption lines across three spectral windows, report preliminary univariate limits of detection between 54 and 583 ppm, and observe that REE lines appear earlier and decay faster in the CRMs than in the alloy. They attribute the temporal differences to matrix effects, particularly oxygen content favoring molecular formation, and conclude that the method resolves individual lines with minimal overlap.

Significance. If the reported line identifications and LODs are reproducible, dual-comb absorption spectroscopy could provide a high-resolution, broadband alternative or complement to emission-based LIBS for real-time REE sensing in exploration and mining contexts. The ability to access both atomic and molecular features simultaneously with sub-GHz resolution in a multi-THz window addresses a recognized limitation of congested LIBS spectra in complex matrices.

major comments (2)

The abstract states that 'preliminary limits of detection from 54-583 ppm are estimated for CRMs, using univariate analysis of selected transitions' and that 'most all REE lines appear earlier and disappear faster in the CRM samples.' No spectra, time-resolved traces, calibration curves, error bars, or statistical measures of fit are supplied, so the quantitative claims and the matrix-effect interpretation cannot be evaluated for baseline artifacts, hidden overlaps, or plasma-condition dependence.
The claim that 'we can resolve individual REE and matrix lines with minimal spectral overlap' is presented as a central advantage over LIBS, yet the manuscript provides neither the line lists nor the three spectral windows with overlaid identifications that would allow assessment of residual blending or assignment .

minor comments (2)

The abstract refers to 'three spectral windows' without specifying their center wavelengths or bandwidths, which are needed to judge coverage relative to known REE transitions.
The phrase 'most all REE lines' is imprecise; a quantitative statement of how many of the observed features were assigned to REEs versus matrix species would strengthen the comparison.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No mathematical model or derivation is present; the work relies on standard assumptions of laser-plasma spectroscopy (local thermodynamic equilibrium, optically thin lines) that are not re-derived here.

pith-pipeline@v0.9.0 · 5644 in / 1147 out tokens · 38339 ms · 2026-05-07T02:26:33.587224+00:00 · methodology

Signatures of rare-earth elements in mineralogical form using laser-ablation dual-comb spectroscopy

Core claim

Load-bearing premise

discussion (0)