LIBS in industrial environments

Laser-induced breakdown spectroscopy focuses a short, high-energy pulse onto a sample, creates a microplasma, and reads the emission as that plasma cools. It provides elemental composition in milliseconds, on almost any material, with no sample preparation. That combination is why it is used on conveyors, at mine faces and beside furnaces.

Requirements on the spectrometer

Broad simultaneous coverage. Elemental emission lines are distributed from the deep UV to the near-IR, and the useful lines for a given matrix are rarely adjacent. This is one of the clearest cases for a dual system, because 200 nm and 800 nm are frequently required in the same shot.

Gated timing. The plasma evolves over microseconds. Immediately after the pulse it is a bright continuum that carries no elemental information. A few microseconds later the atomic lines emerge against a falling background. A spectrometer that cannot be triggered and delayed with respect to the laser is not usable for quantitative LIBS.

Resolution where the interferences are. Many quantitative LIBS problems come down to resolving one line from a neighbor a fraction of a nanometer away.

Requirements on the rest of the installation

These factors decide whether an installation works, and they are rarely on a datasheet:

• Durable optical access. Windows become coated. Any optic viewing a dusty process needs a purge, a shutter or a maintenance schedule that will be kept.
• Standoff geometry. The focus has to land on the sample. On a moving conveyor with varying burden depth, this is a mechanical and control problem rather than an optical one.
• Sample representativeness. LIBS measures a crater a few tens of microns across. On a heterogeneous material such as coal, one shot describes one grain. Useful analysis requires many shots, averaged deliberately.
• Calibration against the real matrix. Plasma formation depends on the material. A calibration built on pressed pellets will not transfer to run-of-mine material without additional work.

None of these is a reason to avoid LIBS. They are reasons to treat the spectrometer as the more straightforward part of the project, which in Evolve Sensing’s experience it usually is.