LIBS in Geosciences: A Practical Tutorial

Introduction

Laser-induced breakdown spectroscopy (LIBS) has moved from the laboratory to the field because it is one of the few current technologies capable of detecting and measuring every element in the periodic table above its intrinsic, material-specific limit of detection (LOD), and because it can provide rapid, in situ elemental fingerprints with almost no sample preparation.^1,2,3 For geoscientists working with minerals, rocks, ores, soils, meteorites, and applications in environmental monitoring and cultural heritage, LIBS bridges the gap between portable X-ray fluorescence (pXRF) and laboratory-based analytical techniques such as electron probe microanalysis (EPMA), atomic absorption spectroscopy (AAS), X-ray fluorescence (XRF), instrumental neutron activation analysis (INAA), inductively coupled plasma–optical emission spectroscopy (ICP-OES), and inductively coupled plasma–mass spectrometry (ICP-MS).⁴ This tutorial briefly illustrates how LIBS works and how it is used in geoscience applications.⁵

Figure 1. LIBS analysis workflow, from field sampling to interpretation. (1) The sample is selected and exposed with minimal or no preparation. (2) A high-energy laser pulse ablates a small amount of material, forming a microplasma. (3) Emitted light is collected through a fiber optic and directed to a spectrometer. (4) The resulting spectrum shows element-specific emission lines, identified qualitatively and quantitatively. (5) Concentrations are calculated using fundamental parameters or calibration, then exported. (6) Mapping point-by-point, line-by-line, or area-by-area is possible, and results can be integrated with field observations and other datasets.

What LIBS Measures

A LIBS system fires a nanosecond laser pulse—typically a 1064 nm, Q-switched Nd:YAG laser with a pulse energy of 10–100 mJ. The pulse duration is 6–15 ns, with a repetition rate adjustable from 5–20 Hz. The pulse ablates ∼0.1–10 µg of material and creates a microplasma at 8,000–30,000 K. As the plasma cools over 1–10 µs, excited atoms emit light at element-specific wavelengths. A spectrometer captures 200–900 nm in a single shot.

Key Strengths for Geoscience Applications

• All elements, from H to U, can be detected in a single LIBS spectrum, whereas XRF misses light elements such as Li, Be, B, C, N, O, and Na.^5,6
• Elements such as Mg, Al, Si, and P are easily detected by LIBS but are absent or weak in the XRF spectrum.
• Depth profiling: Each laser shot removes 0.3–5 µm of sample. Repeated shots on the same spot reveal chemical stratigraphy through weathering rinds, patinas, and fusion crusts.
• Speed: Repetition rates range from 1 Hz to 100 Hz, allowing a thin section to be mapped at 50 µm pixels in minutes.
• Minimal damage: The ablation crater is only 50–300 µm wide, which is acceptable for cultural heritage artifacts.
• Limits: Precision is 3–10% relative standard deviation (RSD), well above the 0.1% typical of ICP-MS.
• Matrix effects are strong, and quantification is difficult without matrix-matched standards.

From Rock to Spectrum: LIBS Sampling Basics and Best Practices

A common practice in laboratory LIBS studies is the analysis of minerals and rocks without any sample preparation. Rocks in the field often show incipient alteration and may be covered with secondary substances such as regolith, atmospheric deposits, aqueous precipitates, and biofilms. Handheld LIBS analyzers enable on-site geochemical analysis through the use of multiple cleaning shots to eliminate surface contamination. Homogeneous samples are simple to analyze, but inhomogeneous samples present challenges.^3,4

• Clean the sample surface to remove dust or the weathering rind. Fresh fractures or polished faces provide reproducible spectra. Use flat, stable samples >1 cm to avoid edge effects and movement during ablation. For soils, press pellets at a load of >5 metric tons to ensure homogeneity.
• Avoid moisture; dry samples at 40–60 °C if needed. Wet samples cause plasma instability and low signal.
• For heterogeneous rocks, map multiple spots across minerals, veins, and matrix. A minimum of 10–20 shots per spot is needed to average out heterogeneity.
• Maintain consistent laser focus and energy and document spot locations with photographs for reproducibility.
• Always run standards before and after samples to monitor drift and enable quantification.
• Use argon purging for C, S, Cl, and P. Use a delay time of 1 µs for major elements and 2 µs for trace elements to allow continuum background emission to decay. Use 5–10 shots for surface analysis, but keep single-shot logs for depth profiling.
• Eye safety: This is a Class 4 laser; use laser safety goggles, a beam enclosure, and interlocks.
• Data: Save full spectra for later processing.

Table 1. Diagnostic LIBS Emission Lines for Elements Commonly Encountered in Geological Materials

Rule: Fe lines are ubiquitous in most geological samples. In Fe-rich samples, select lines >400 nm to avoid interference in the ultraviolet region.

Table 2. Instrument Hardware Considerations for Geoscience LIBS Applications

Quantification: From Intensities to Weight Percent

LIBS is not inherently quantitative because the plasma excitation temperature (T_e) and electron density (N_e) change with the sample matrix.^3,7

Four approaches to elemental quantification are commonly used in geoscience LIBS:

(a) Univariate Calibration with Matrix-Matched Standards

This approach is best for a single element, for example, Li in pegmatite. Prepare five pressed pellets of Li ore with 0.1–4% Li of the same rock type, then plot the intensity of the Li 670 nm line against wt % Li. Precision is approximately 5–15%.

(b) Internal Standardization

This method assumes that all elements produce the same total plasma intensity. One major element is chosen as an internal standard (IS); for example, Fe can serve as the IS, such that:

C_Ni = k × (I_Ni / I_Fe) × C_Fe [1]

where C_Ni and C_Fe are the concentrations of Ni and Fe, I_Ni (341.48 nm) and I_Fe (371.99 nm) are the corresponding emission line intensities, and k is an empirical proportionality (calibration) constant.

This method works well if Fe is constant or independently measured, but it fails if the Fe 371.99 nm line saturates.

(c) Calibration-Free LIBS (CF-LIBS)

This method uses a Boltzmann plot, in which E_upper is plotted against ln(Iλ / gA) for several Fe lines, where the measured line intensity I of a given transition is related to the plasma parameters by:

ln(Iλ / gA) = −E_upper / (k_BT_e) + ln(N / U(T_e)) [2]

where I, λ, g, and A are the intensity, wavelength, upper-level statistical weight, and transition probability of the line; E_upper is the upper-level energy; k_B is the Boltzmann constant; T_e is the plasma excitation temperature; N is the total number density of the emitting species; and U(T_e) is the partition function at T_e.

The slope of the plot gives T_e. The plasma electron number density (N_e) is determined by analyzing the Stark broadening of a well-isolated emission line; the most reliable line for this purpose is the H-α line at 656.28 nm. The concentration of each element is then calculated; no standards are needed. Accuracy is typically 10–30%. This method requires clean Fe lines and the assumption of local thermodynamic equilibrium (LTE).²

After the concentration of each element is calculated, the values are summed to 100%. If the sum exceeds 100%, self-absorption may have occurred or the wrong internal standard may have been used; all values are then scaled down proportionally.

(d) Chemometric Approaches in LIBS

LIBS data are well suited to chemometric processing because they reflect elemental concentrations and molecular and isotopic abundances, producing large datasets with 1–2 × 10⁴ intensity–wavelength data points spanning 190 to 900 nm. Chemometrics aids LIBS data analysis by addressing the complex, nonlinear broadband emission spectra that result from various plasma emission factors.

Studies classifying geological media typically use principal component analysis (PCA) for exploratory data analysis and partial least squares regression (PLSR), partial least squares discriminant analysis (PLS-DA), soft independent modeling of class analogy (SIMCA), and k-nearest neighbors (KNN) for sample discrimination. Table 3 compares pXRF to hLIBS for various analysis applications.

Table 3. Field Use: What Handheld LIBS Adds to Portable XRF

Both techniques are complementary in practice: use pXRF for accurate Ca, K, and Zr, and LIBS for Li, B, C, F, Na, and stratigraphy—with no cutting, acid, or laboratory required.

Common Pitfalls in Geoscience LIBS and Solutions

• Self-Absorption: Flattens the calibration curve at high concentrations and produces artificial spikes in other elements. Solution: Use a weaker line, for example, Fe 404.58 nm instead of 371.99 nm for >70% Fe.
• Chemical Matrix Effects: A silica-rich rock produces a hotter plasma than an iron oxide, so the same wt % Mg gives roughly twice the intensity. Solution: Group samples by rock type.
• Physical Matrix Effects: Grain size changes the ablated mass; coarse sandstone ablates less material than fine mudstone. Solution: Grind to <50 µm and pelletize or accept semi-quantitative data.
• Water Content: A water content of 5% reduces signal intensity by 50%. Solution: Use dry samples or double-pulse LIBS.
• Dust on Optics: Causes the signal to drop from shot to shot. Solution: Normalize the intensity of each element to the total intensity for each shot.

Where LIBS Is Going in Geosciences

LIBS instruments are deployed on the planetary rovers ChemCam, SuperCam, MarSCoDe, and Pragyan, operating at 7–10 m standoff over 240–850 nm and analyzing Martian and lunar rocks (at approximately 20 cm standoff) daily.³ Next-generation handheld instruments add Raman spectroscopy and laser-induced fluorescence (LIF) for mineralogy. Machine learning applied to full spectra outperforms peak-area quantitation for complex matrices. Machine learning accelerates LIBS analytical frameworks by linking spectral features with chemical composition, yielding meaningful classification and quantitative results when properly validated. It is not, however, a universal solution, and continued technological advancement remains essential for LIBS geochemical applications.³

Bottom line: at present, LIBS cannot replace EPMA or ICP-MS for accuracy, but it is unmatched for rapid, spatial, and light-element data acquisition on rocks, soils, and metals, especially for depth resolution.

Learn the underlying plasma physics, respect self-absorption, choose the intensity line wisely, and get geological answers directly in the field, not weeks later.

References

(1) Senesi, G. S. Laser-Induced Breakdown Spectroscopy (LIBS) Applied to Terrestrial and Extraterrestrial Analogue Geomaterials with Emphasis to Minerals and Rocks. Earth-Sci. Rev. 2014, 139, 231–267. DOI: 10.1016/j.earscirev.2014.09.008

(2) Fabre, C. Advances in Laser-Induced Breakdown Spectroscopy Analysis for Geology: A Critical Review. Spectrochim. Acta B: At. Spectrosc. 2020, 166, 105799. DOI: 10.1016/j.sab.2020.105799

(3) Harmon, R. S.; Senesi, G. S., Eds. Laser-Induced Breakdown Spectroscopy (LIBS): A 21st Century Analytical Tool for the Geosciences, 1st ed.; Cambridge Scholars Publishing, 2026. ISBN: 978-1-0364-6872-9.

(4) Senesi, G. S.; Harmon, R. S.; Hark, R. R. Field-Portable and Handheld LIBS: Historical Review, Current Status, and Future Prospects. Spectrochim. Acta B: At. Spectrosc. 2021, 175, 106013. DOI: 10.1016/j.sab.2020.106013.

(5) Harmon, R. S.; Senesi, G. S. Laser-Induced Breakdown Spectroscopy—A Geochemical Tool for the 21st Century. Appl. Geochem. 2021, 128, 104929. DOI: 10.1016/j.apgeochem.2021.104929

(6) Harmon, R. S.; Fabre, C.; Senesi, G. S. Laser-Induced Breakdown Spectroscopy. In Treatise on Geochemistry, 3rd ed.; (Eds. Anbar A. D. and Weis D.), Elsevier, 2025; Vol. 8, pp 607–644. DOI: 10.1016/B978-0-323-99762-1.00003-6

(7) Harmon, R. S.; Senesi, G. S. Laser-Induced Breakdown Spectroscopy (LIBS). Geostandards Geoanal. Res. 2024, 48, 763–792. DOI: 10.1111/ggr.12560

About the Author

Giorgio S. Senesi

Dr. Giorgio S. Senesi is a geologist and senior researcher at the Italian National Council Research and Institute for Plasma Science and Technology in Bari, Italy. He holds a BA/MS in Vulcanology and PhD in Earth Sciences from University of Bari. He has been a Post-Doctoral Fellow at the Department of Plant and Soil Sciences at the University of Delaware in Newark in the USA and a researcher at the Centro Laser of Valenzano in Bari. He is co-Editor of the 2023 book African Meteorites by Bentham Books and of the 2026 book Laser-Induced Breakdown Spectroscopy: A 21^st Century Analytical Tool for the Geosciences by Cambridge Scholars Publishing. He holds an Honorary Membership of the University Museum of Meteorites in Morocco. http://orcid.org/0000-0002-3947-6853