Exploring the Unknown:The Spectral Power of Pulsed Lasers (LIBS)

Principle of LIBS

The fundamental principle of Laser-induced Breakdown Spectroscopy (LIBS) involves using a laser to induce plasma on the surface or within the sample. The emitted spectrum from this plasma is collected and analyzed for its wavelengths and intensities, allowing for the qualitative or quantitative determination of the sample's properties. The primary instruments required for these measurements include a pulsed laser and a spectrometer.

Figure 1: Schematic diagram of laser induced breakdown spectroscopy( LIBS)

Based on the positions of the characteristic spectral lines of elements, the composition of the sample can be qualitatively analyzed. Furthermore, quantitative analysis of the elemental content can be performed. The basic principle relies on the Boltzmann equation. Under local thermal equilibrium conditions, the intensity of the characteristic spectral lines emitted by the plasma, due to the transition from the upper energy level i to the lower energy level j, can be expressed as:

I_{i j}=F n_{s} \frac{n^{I}}{n^{I}+n^{I I}} \frac{g_{i} \exp \left(-E_{i} / k_{B} T\right)}{U(T)} A_{i j}

where $I_{ij}$ is the intensity of the characteristic spectral line; $F$ is an instrument response parameter related to the detection efficiency; $n_s$ is the total particle number density of the detected element; $n_I$ and $n_{II}$ are the number densities of the element's neutral atoms and singly ionized ions, respectively; $g_i$ , $E_i$ , $U(T)$ , and $A_{ij}$ are the degeneracy of the upper energy level $i$ , the energy of the upper energy level $i$ , the partition function, and the spontaneous transition probability between the two energy levels, respectively.

From the above equation, it can be seen that when the plasma temperature $T$ , electron density $n_e$ , and instrument response parameter $F$ remain constant, the intensity of the element's characteristic spectral line is proportional to its total particle number density $n_s$ . Under the assumption of stoichiometric ablation, the latter is also proportional to the concentration $C_s$ of the element $s$ in the sample, that is:

I_{ij} = k C_s

Furthermore, based on this principle, a univariate calibration model can be established between the intensity of the elemental spectral line and the element concentration. This forms the basis for quantitative analysis using LIBS.

Principle of LIBS Laser-Induced Breakdown Spectroscopy

LIBS stands for Laser-Induced Breakdown Spectroscopy. Its working principle involves using a pulsed laser to generate plasma, which ablates and excites the material in a sample (typically a solid). The spectrometer then captures the spectrum emitted by the atoms excited by the plasma. This spectrum is used to identify the elemental composition of the sample, enabling material identification, classification, qualitative, and quantitative analysis.

As a novel technique for material identification and quantitative analysis, LIBS can be used both in laboratories and for online industrial field detection.

Figure 2: LIBS Principle Diagram

Industry Applications of LIBS Laser-Induced Breakdown Spectroscopy

Due to the advantages of LIBS technology,such as rapid and direct analysis with minimal sample preparation, the ability to detect almost all elements and simultaneously analyze multiple elements, cleaning sample surfaces from oxides and dust layers, enabling layer-by-layer analysis, and accommodating a wide range of sample matrices,it is capable of detecting nearly all solid samples and can be used for remote sensing and on-site analysis. LIBS thus addresses the shortcomings of traditional elemental analysis methods, offering significant advantages particularly in applications such as micro-area material analysis, coating/film analysis, defect detection, jewelry identification, forensic evidence identification, powder material analysis, and alloy analysis.

Moreover, LIBS has broad applicability in various fields including petroleum exploration, hydrology and geological exploration, metallurgy and combustion, pharmaceuticals, environmental monitoring, scientific research, military and defense, and aerospace.

Advantages of LIBS

Rapid analysis, in-situ detection, minimal or no sample pre-treatment required, capability to analyze a wide variety of elements, and small spot detection area, among others.