Plasma optical emission signal characterisation in Laser-Induced Breakdown Spectroscopy

The interaction of high-intensity laser pulses with a sample can result in the formation of a short-lived plasma. From the deexciation of the plasma, we can extract information about the chemical composition of the target using a spectrometer. This technique is known as Laser-Induced Breakdown Spectroscopy (LIBS).

LIBS has attracted growing attention in different areas and applications for its ability to perform real-time, on-site and non-destructive elemental analysis across a wide range of materials. Nevertheless, its analytical performance is often limited by significant signal variability and reduced reliability.

In this work, the plasma optical emission signal was successfully characterised under the influence of various experimental conditions by studying their effect on signal intensity and measurement variability. The analysis was conducted on a dedicated test bench and is structured into two main sections: plasma generation and plasma optical emission collection. The main results showed that, for ultrashort pulse durations at pulse energies close to the breakdown threshold, the signal intensity varies linearly.

Regarding the focusing conditions, the analysis revealed the existence of two maxima, and a slight defocus was shown to improve plasma generation. Concerning signal collection, an optimal magnification that maximizes the collected emission was found. Additionally, the impact of the chromatic focal shift was verified and the isotropic nature of the plasma emission was demonstrated.