Laser-Induced Breakdown Spectroscopy (LIBS) is a technique used in analytical chemistry and material science to determine the elemental composition of a sample. It utilizes a process called laser-induced breakdown, where a high-energy laser pulse is focused onto the surface of the sample, generating a plasma plume. This plasma plume emits characteristic light or radiation, which is then analyzed to identify and quantify the elemental constituents present in the sample.
Every laser-induced breakdown spectrum encompasses valuable details regarding the concentrations of naturally occurring and artificially produced elements, as well as certain isotopic ratios and information concerning the atomic structure of the material being analyzed. LIBS is a method of spot analysis, wherein laser ablation creates craters (holes or cavities) ranging from 30 µm to 400 µm in diameter, depending upon factors such as the laser wavelength, output power, properties of the material, and the efficiency of laser-material interaction. As LIBS operates as a spot analysis technique, it evaluates spatial variations in material composition. It also allows for the averaging of multiple shots obtained from different locations on the material, thereby providing a representation of its bulk composition.
Principles of Laser-Induced Breakdown Spectroscopy
The principle of Laser-Induced Breakdown Spectroscopy (LIBS) uses a powerful laser pulse to heat the sample surface which creates a hot plasma. This plasma contains atoms and molecules that are excited by the high temperature. As the plasma cools down, the excited electrons in the atoms and molecules return to lower-energy states, releasing photons.
The wavelengths of these emitted photons correspond to the energy differences between the excited and base energy states. Each element and even different isotopic compositions of molecules have their own unique set of energy states and, consequently, emit photons at specific wavelengths. By measuring the emitted wavelengths of light, we can identify the elements present in the sample and even determine isotopic ratios using a technique called Laser-Induced Molecular Isotopic Spectrometry.
Working of Laser-Induced Breakdown Spectroscopy
LIBS systems use a range of lasers, with the Nd:YAG laser being the most common. These lasers operate at different wavelengths, such as 1064 nm, 266 nm, or 213 nm. The pulse widths of these lasers typically fall within the range of 6 to 15 nanoseconds, while the repetition rates can vary.
When the laser beam is focused on the sample surface, a small amount of material is ablated or removed, known as Laser Ablation. This ablated material then interacts with the trailing portion of the laser pulse, resulting in the formation of a highly energetic plasma containing free electrons, excited atoms, and ions.
As the laser pulse ends, the plasma begins to cool down. During this cooling process, the excited electrons in the atoms and ions return to their lower energy states, emitting light with specific spectral peaks. This emitted light is collected by a lens located near the plasma and transmitted to a spectrometer through a fiber optic cable. The spectrometer, often equipped with an ICCD (Intensified Charge-Coupled Device) or spectrograph detector module, analyzes the LIBS spectrum.
Inside the spectrometer, the light interacts with a diffraction grating, which separates it into its component wavelengths or colors, allowing for classification. These wavelengths or colors are subsequently transmitted to the detector, where they generate spectral data. The spectral data is then sent to the CPU for analysis.
Each element in the periodic table has its own unique set of spectral peaks in LIBS analysis. By identifying and studying these different peaks for the analyzed sample, the chemical composition of the sample can be rapidly determined. Additionally, the intensity of the LIBS spectral peaks can provide information about the concentration of both trace and major elements present in the sample.
Advantages of Laser-Induced Breakdown Spectroscopy
Limitations of Laser-Induced Breakdown Spectroscopy
Applications of Laser-Induced Breakdown Spectroscopy
LIBS has applications in different industries and scientific domains.
It is used in environmental monitoring, enabling rapid and on-site analysis of soil, water, and air samples. It facilitates the identification and quantification of contaminants, such as heavy metals, pollutants, and toxic elements, aiding in environmental risk assessment and remediation efforts. LIBS also allows for real-time monitoring of emissions in industrial settings, contributing to improved air quality control.
LIBS provides valuable information for material characterization in fields such as metallurgy, geology, and archaeology. It enables the identification and analysis of elements and compounds present in metals, minerals, ceramics, and ancient artifacts. LIBS can assist in assessing material quality, identifying impurities, determining alloy composition, and studying the provenance of archaeological objects.
It has applications in the pharmaceutical industry, particularly in the analysis of raw materials, drug formulations, and counterfeit detection. This spectroscopy enables rapid screening for elemental impurities and ensures compliance with regulatory standards. LIBS contributes to quality control processes, assisting in the verification of drug authenticity and ensuring the safety and efficacy of pharmaceutical products.
In the aerospace and defense sectors, LIBS plays a significant role in applications such as aerospace materials analysis, surface coating evaluation, and forensic investigations. It facilitates the identification and analysis of elements in aircraft components, including alloys, composites, and coatings. LIBS also aids in detecting trace elements, explosives, and chemical warfare agents, supporting forensic analysis and security assessments.
LIBS has gained importance in art restoration and cultural heritage studies. It helps conservators identify pigments, coatings, and surface treatments used in artworks, providing insights into the artist's techniques and aiding in restoration efforts. LIBS analysis allows for the evaluation of the impact of environmental factors on artifacts, assisting in their preservation and conservation.
In the mining industry, LIBS offers a rapid and non-destructive method for assessing the elemental composition of rocks, ores, and minerals. It aids in mineralogical mapping, identifying valuable mineral deposits, and determining the presence of impurities or contaminants. LIBS can also support geological exploration efforts by providing real-time analysis in the field, facilitating decision-making processes.
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