Measurement error due to self-absorption in calibration-free laser-induced breakdown spectroscopy

Area of Science:

• Analytical Chemistry
• Atomic Spectroscopy
• Plasma Physics

Background:

• Self-absorption of spectral lines degrades analytical measurement performance in calibration-free laser-induced breakdown spectroscopy (CF-LIBS).
• The precise error growth associated with self-absorption remains inadequately quantified, hindering accurate elemental analysis.

Purpose of the Study:

• To develop and validate a method for quantifying measurement errors caused by self-absorption in CF-LIBS.
• To elucidate the influence of spectral line shape and intensity measurement techniques on self-absorption-induced errors.

Main Methods:

• Calculated spectral radiance of a plasma in local thermodynamic equilibrium.
• Performed spectroscopic measurements on a binary alloy thin film with a compositional gradient.
• Validated the proposed error quantification method against experimental data.

Main Results:

• Measurement performance degradation due to self-absorption is dependent on the spectral transition's shape and the chosen intensity measurement method.
• Line-integrated intensity measurements of Stark-broadened lines provide accurate analysis even with high optical thickness, provided line width and plasma size are known.
• Error growth is substantially larger for Doppler-broadened lines and line-center intensity measurements.

Conclusions:

• The developed method accurately quantifies self-absorption errors in CF-LIBS.
• Findings guide the selection of optimal analytical lines to minimize self-absorption effects.
• This advance improves the reliability of compositional measurements using CF-LIBS.