Approach to detection in laser-induced breakdown spectroscopy.

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.

Hyphenation of a near-infrared Echelle spectrometer to a microplasma for element-selective detection in gas chromatography.

The coupling of a near-infrared Echelle spectrometer (NIRES) with a gas chromatograph for element-selective detection is introduced. The miniaturized capacitive plasma device is operated at a frequency of 40.68 MHz and is mounted directly on an Hewlett-Packard HP6890 GC. First results with a mixture of halogenated standard compounds are presented and discussed in terms of the advantages and problems with this system.

Adaptation of an echelle spectrograph to a large CCD detector.

A broad range echelle spectrograph with a CCD matrix detector is developed for different applications in atomic spectroscopy. The compact optical design in combination with a dispersive entrance slit illumination offers a low stray light level and high throughput in the UV spectral region comparable only with spectrographs of higher focal length. Ray tracing calculations for typical wavelengths and the multi-line spectrum of an iron arc show the excellent overall spectrum quality. The subtraction of two partial spectra of different steel alloys demonstrates the spectra evaluation possibilities of the CCD spectrograph.

Influence of the spectral bandwith of the spectrometer on the sensitivity using continuum source AAS.

The influence of the spectral bandwidth of the spectrometer on the performance of the spectrometer is of great importance in atomic absorption spectrometry using continuum source (CS-AAS). For a theoretical analysis of the detection of small absorbances two cases have to be taken into account: as long as the limiting noise of the signal is given by the detector noise an increase in spectral bandwidth of the spectrometer implies an improvement in the limit of detection. In contrast, if the noise of the signal is dominated by the photon shot noise the detection limit should become independent of the spectral bandwidth. In this case the spectral bandwidth of the spectrometer should be chosen equal to the bandwidth of the absorption line to avoid spectral interferences. Theoretical calculations are presented for the dependence of the characteristic mass on the spectral bandwidth in case of CS-AAS measurements. The results are compared with experimental measurements for six different elements using continuum source as well as line sources. The investigations were done using a double echelle monochromator (DEMON) which offers a high spectral resolution lambda/Deltalambda of about 140,000.