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LIBS Basics & Applications
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LIBS Application Notes (click) |
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What is LIBS?Laser-Induced Breakdown Spectroscopy (LIBS) is a spectroscopic technique using a laser-generated plasma to ablate and excite a sample, which can initially be in solid, liquid, or gaseous form. Emission generated from the plasma is used to identify material constituents and can be used to identify, sort, and classify materials. What can LIBS be used for?LIBS can be used both in-process and in the laboratory for material identification. A very versatile method, it has the primary advantages of:
How does LIBS work?Laser-Induced Breakdown Spectroscopy utilizes a focused pulse from a high-powered laser to create a plasma in or on a solid, liquid, or gaseous media. Some of the energy in the plasma is used to ablate solid or liquid material (if present), and the plasma rapidly expands to form a gas plasma which is used to analyze the ablated particles. In the core of the plasma, effective temperatures can easily exceed 50,000 K or several eV. During this stage, material in the core of the plasma is vaporized and atomized, and the plasma is typically highly ionized. Depending on conditions, but typically after 0.5 – 1 microseconds, the neutral states of the plasma typically reach local thermodynamic equilibrium. From this time onward, upper electronic states of atoms are thermally populated in Boltzmann equilibrium, such that the emission intensity of the atomic fluorescence I ~ exp(E/kT), where E is the upper state energy level of the fluorescing species. As the plasma cools, continuum emission from the plasma (Bremstraalung emission, which we see as bright white emission) fades, typically much faster than emission lines from neutral and singly-ionized atomic lines, such that each elemental emission line has a particular optimum in a particular plasma. This optimum depends on the time and temperature history of the plasma, which in turn is dependent on the laser pulse energy and pulse length. For typical 50 – 400 mJ, ~10 ns pulses, the sequence of events in the plasma is shown below; in higher-energy, longer-pulse plasmas, events are shifted to longer times, while for lower energy, shorter-pulse plasmas, events are at shifted to shorter times. The emission from the spectra can be then quantified and calibration curves can be obtained by standard peak integration or by use of chemometrics, and/or pattern-matching routines can fingerprint the material to determine its type. |
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| The time-line of the plasma. | |||||||||
