![]() ![]() Emission enhancement was investigated as a function of both time acquisition delay and inter-pulse delay. Re-excitation was conducted using a nanosecond laser emitting at 1064 nm that induced air breakdown 1 mm above the target. The analysis was performed by applying a 266 nm pulsed laser devised to minimize sample damage. Films were grown through nanosecond pulsed laser ablation over silicon and glass substrates. Orthogonal reheating double-pulse laser-induced breakdown spectroscopy (LIBS) was applied to the elemental analysis of CdTe thin film samples. It was shown that the pre-ablation causes an increase of ablation crater dimensions and the re-heating increases the plasma temperature. To explain this effect, the dimensions of ablation craters were measured for each configuration using a 3D optical microscope and the temperature was determined from the slope of Boltzmann plot. It has been shown that the spectral lines with higher value of excitation energy prove higher enhancement in both DP LIBS and 3P LIBS configurations. In addition, the relationship of signal enhancement and the upper-level energy of selected spectral lines was studied. The 3P LIBS results showed up to 5-fold improvement of the signal to background ratio compared with both DP LIBS arrangements and up to 228-fold improvement in comparison to conventional SP LIBS. ![]() The interpulse delays for both DP LIBS and for 3P LIBS configurations were optimized separately in order to obtain the highest possible enhancement for each of them. All possible configurations were studied - single pulse, pre-pulse DP LIBS, re-heating DP LIBS and triple-pulse LIBS. This energy as well as the energies of the pre-ablation and the re-heating laser pulses were kept constant for all experimental arrangements. It means that energy of ablation laser pulse was set to the minimal value for which the intensities of selected spectral lines were above the limits of detection. The experiment was designed with the emphasis to a minimal sample damage. Namely, the pre-ablation laser pulse and re-heating laser pulse were combined into the triple-pulse LIBS (3P LIBS) to achieve the plasma emission enhancement. The goal of this work is to examine the effect of third additional laser pulse on the orthogonal double-pulse laser-induced breakdown spectroscopy (DP LIBS) experiment. This approach can potentially be applied for real-time trace monitoring in manufacturing processes of photovoltaic devices where conversion efficiency depends strongly on impurities’ concentration. Therefore, this approach was applied to three unknown polycrystalline silicon solar cells, which yield Al, C, Ca, Fe, In, Ti, Sb and Sn in the parts per million (ppm). It is worth mention that the variant CF-LIBS results, but the approach is simpler and faster. The results are compared with reference values as well as conventional CF-LIBS results, which show that conventional and variant CF-LIBS results are similar and in close agreement to reference values. The Plasma temperature, determined using Boltzmann plot, was used to determine the concentration of all species present in a sample. The double pulse laser induced plasma was produced on the sample surface and the emission spectra were recorded at optimized interpulse delay and energy ratio. We applied variant of calibration free laser induced Breakdown Spectroscopy (CF-LIBS) approach for the compositional analysis of standard Gd/Ge/Si alloy and solar cells.
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