Gated detection with intensified detectors, e.g., ICCDs, is today the accepted approach for detection of plasma emission in laser-induced breakdown spectroscopy (LIBS). However, these systems are more cost-intensive and less robust than nonintensified CCDs. The objective of this paper is to compare, both theoretically and experimentally, the performance of an intensified (ICCD) and nonintensified (CCD) detectors for detection of plasma emission in LIBS. The CCD is used in combination with a mechanical chopper, which blocks the early continuum radiation from the plasma. The detectors are attached sequentially to an echelle spectrometer under the same experimental conditions. The laser plasma is induced on a series of steel samples under atmospheric conditions. Our results indicate that there is no substantial difference in the performance of the CCD and ICCD. Signal-to-noise ratios and limits of detection achieved with the CCD for Si, Ni, Cr, Mo, Cu, and V in steel are comparable or even better than those obtained with the ICCD. This result is further confirmed by simulation of the plasma emission signal and the corresponding response of the detectors in the limit of quantum (photon) noise.
Echelle spectrometers enable the observation of large spectral windows with high resolving power in single recordings. However, these devices are strongly sensitive to temperature variations and even small changes may tamper both the wavelength and the intensity calibration. Here we propose a method for rapid checking and rectifying the calibration using the emission of a plasma produced by pulsed laser ablation of steel. A spectrum recorded with a large delay between the laser pulse and the observation gate exhibits sharp lines that are exploited for wavelength calibration. A second spectrum is recorded with a shorter delay, when the plasma properties enable the accurate simulation of the plasma emission spectrum. The apparatus response is deduced from the ratio of measured over computed line intensities. The method is of particular interest for laser-induced breakdown experiments in which the calibration measurements are performed via the simple change of the irradiated sample.
In this study, a method is presented to measure precisely the thickness of coated components based on laser-induced breakdown spectroscopy (LIBS). The thickness is determined by repetitively ablating the coating with ultrashort laser pulses, monitoring the spectrum of the generated plasma and calculating the coating thickness from the specific plasma signal in comparison to a reference measurement. We compare different pulse durations of the laser (290 fs, 10 ps, 6 ns) to extend the material analysis capabilities of LIBS to a real thickness measurement tool. The method is designed for production processes with known coating materials. Here, we show this for a nickel coating and a tungsten carbide coating on a copper sample with thicknesses from 5–30 µm.
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