COMPARATIVE ELEMENTAL ANALYSIS OF SILKY WHITE AND BLACK MARBLE USING LASER-INDUCED BREAKDOWN SPECTROSCOPY

Abstract

Laser-Induced Breakdown Spectroscopy (LIBS) is used for the elemental analysis of natural geological samples under atmospheric pressure. Plasma is generated using a Q-switched Nd:YAG laser operating at 1064 nm with a pulse duration of 5 ns, a repetition rate of 10 Hz, and a pulse energy of 400 mJ. The recorded emission spectra revealed the presence of calcium (Ca), magnesium (Mg), potassium (K), and barium (Ba) in both marble samples. To obtain representative spectra, multiple laser shots were acquired at different spatial locations on each sample and averaged. Plasma diagnostics were performed to investigate the temporal evolution of the laser-induced plasma. The electron temperature was determined using the Boltzmann plot method under the assumption of local thermodynamic equilibrium (LTE). The maximum electron temperature for Silky White Marble was 23,171.33 K at a delay time of 279 ns, whereas that for Black Marble was 16,203.78 K at 285 ns. The electron number density, estimated from the Stark broadening of the Ca II emission line at 393.36 nm, exhibited a decreasing trend with increasing delay time. For Silky White Marble, the electron number density decreased from 8.402 × 10¹⁶ cm⁻³ to 6.13 × 10¹⁶ cm⁻³, while for Black Marble it decreased from 8.21 × 10¹⁶ cm⁻³ to 5.99 × 10¹⁶ cm⁻³. The plasma frequency, calculated from the electron number density, also decreased with increasing delay time, confirming its direct dependence on electron density. These results demonstrate the capability of LIBS for rapid elemental analysis and plasma diagnostics of marble samples.