S. Palanco

Test of a stand-off laser-induced breakdown spectroscopy sensor for the detection of explosive residues on solid surfaces

The detection and characterization of energetic materials at distances up to 45 m using stand-off laser induced breakdown spectroscopy (LIBS) has been demonstrated. A field-portable open-path LIB spectrometer working under a coaxial configuration was used. A preliminary study allowed choosing a single-pulse laser source over a double-pulse system as the most suitable source for the stand-off analysis of organic samples. The C2 Swan system, as well as the hydrogen, oxygen and nitrogen emission intensity ratios were the necessary parameters to identify the analyte as an organic explosive, organic non-explosive and non-organic samples. O/N intensity ratios of 2.9 and 2.16 with relative standard deviations of 4.03% and 8.36% were obtained for 2,4-dinitrotoluene and aluminium samples, respectively. A field test with known samples and a blind test were carried out at a distance of 30 m from the sample. Identification of energetic compounds in such conditions resulted in 19 correct results out of 21 samples.

Nanometric range depth-resolved analysis of coated-steels using laser-induced breakdown spectrometry with a 308 nm collimated beam

The spatial profile from an XeCl excimer laser was modified using a simple two-lenses telescope to generate a flat energy-profile beam that impinged a layered sample (a Zn-coated steel) without beam conditioning. The irradiance obtained (about 107 W cm–2) was high enough to vaporize the target, to cause plasma formation and to allow atomic emission spectrometry with acceptable signal-to-noise ratio. Modification in beam energy distribution resulted in flat ablated profiles and improved depth-resolution up to the few nm pulse–1 range was attained. The net intensity areas were transformed into normalized values leading to plots in excellent agreement with those provided by commercial depth-resolved analysis instruments.

Open-path laser-induced plasma spectrometry for remote analytical measurements on solid surfaces

a ´´ Abstract Open-path laser-induced plasma spectrometry has been studied for elemental analysis at a distance of 45 m from the target. The 230-mJ pulsed radiation of a Q-switched Nd:YAG laser at 1064 nm has been used to produce a plasma on the sample and light emission has been collected under an off-axis open-path scheme. Under such conditions, the main variables influencing the signal response such as beam focal conditions, laser incidence angle and laser penetration depth have been identified and diagnosed on the basis of spectral signal-to-noise ratio considerations. The incidence angle is critical beyond 608. Crater morphology and ablation rates have been studied also. A semi-quantitative analysis of several stainless steel grades has been implemented using a pattern recognition algorithm, which allowed to discriminate successfully the samples on the basis of their variable content in alloying elements. 2002 Elsevier Science B.V. All rights reserved.

Quantitative analysis of low-alloy steel by microchip laser induced breakdown spectroscopy

The development of a compact laser induced breakdown spectroscopy (LIBS) system increases the possibilities of applying the technique in industrial arenas, field applications and process monitoring. Significant progress has been achieved in miniaturization of optical detectors and lasers, allowing portable, low-cost LIBS equipment to be devised. Conventional lasers for LIBS, like actively Q-switched Nd:YAG lasers are limited by their bulkiness, the need for a cooling system and high power consumption. The use of a miniature solid state microchip laser overcomes these drawbacks and offers further advantages of good beam quality, high pulse repetition frequency and less damage to target. In this work we studied the quantification of elemental composition of low alloy steel samples using a higher power microchip (“powerchip”) laser. The possibility of real time, in situ quantification of such materials by powerchip LIBS enhances the applicability of the technique to process monitoring in the steelmaking industry. The performance of the LIBS technique based on a powerchip laser and a portable non-intensified, non-gated detector for elemental quantification is evaluated and compared to that obtained using an intensified detector. Calibrations were achieved for Cr, Mo, Ni, Mn and Si with linear regression coefficients between 0.98–0.99 and limits of detection below 100 ppm in most cases.

Portable instrument and analytical method using laser-induced breakdown spectrometry for in situ characterization of speleothems in karstic caves

A portable laser-induced plasma spectrometer has been developed and tested in the determination of thickness and semi-quantitative composition of alteration layers on the surface of speleothems. The portable instrument consists of a 50 mJ pulse −1 Q-switched Nd:YAG laser operating at 1064 nm and a high resolution spectrometer equipped with a 2048-element linear silicon CCD array detector. Its weight and size allow in situ analysis in difficult environments or relatively inaccesible places such as caves, avoiding sample collection or extraction. The instrument was evaluated in the interior Nerja Cave (Spain) over soils, rocks and speleothems. The geochemical degradation of these materials has been studied by the portable instrument. Laser-induced plasma analysis reveals the remarkable presence of several elements in the surface of the speleothems, such as Fe, Si, Al or Mn which are absent in non-degraded regions of the speleothem. Composition depth profiles of these elements have been measured in order to evaluate alteration processes in the Nerja Cave.

Remote laser-induced plasma spectrometry for elemental analysis of samples of environmental interest

Remote laser-induced plasma spectrometry has been demonstrated as a valuable analytical tool both for qualitative inspection and quantitative determinations on environmental samples. For this objective, the pulsed radiation of a Q-switched Nd:YAG laser at 1064 nm has been used to produce a plasma in a remote sample, the light emission being collected under a coaxial open-path optical scheme and guided towards a spectrograph and then detected by an intensified CCD. A prospective study has been carried out to assess the suitability of the technique for the remote analysis of samples from a coastal scenario subjected to a high industrial activity. All the measurements have been done in the laboratory. Among the main factors influencing the analytical results, sample moisture and salinity, sample orientation and surface heterogeneity have been identified. The presence and distribution of Fe and Cr as a contaminant on sample surface has been quantified and discussed for samples including soil, rocks, and vegetation. At a stand-off distance of 12 m from the spectrometer to the sample, limits of detection in the order of 0.2% have been obtained for both elements.

Analytical control of liquid steel in an induction melting furnace using a remote laser induced plasma spectrometer

An open-path laser-induced plasma spectrometer (OP-LIPS) has been designed, built and demonstrated under factory conditions. The system, built in the University of Malaga, was transported and installed at the on-line control laboratory of a stainless steel factory. A laboratory-scale induction furnace of 1 kg capacity was used for the tests. OP-LIPS has proved to be a reliable technique capable of discriminating changes produced in hot-solid and liquid stainless steel composition. Under these conditions, OP-LIPS has been shown of particular value, evidencing its capability to reveal surface composition changes on-line, and with real-time response at very high-temperatures.

Spectroscopic diagnostics on CW-laser welding plasmas of aluminum alloys

Abstract In-process diagnostics intended to correlate spectrometric measurements to the occurrence of laser welding defects such as notches and blowholes have been carried out. The plasma light emitted during high-power CO2 laser welding of a 6013 aluminum alloy was guided to an imaging spectrograph and the dispersed light was detected with a CCD system. A transient recorder was used to record the signal from a fast laser-power monitor and the sync signals from the CCD and a fast speed video camera. Accuracy of the measurements are discussed in relation to the low and fast acquisition rate approaches (58 spectra s−1 and 4×103 spectra s−1, respectively) used in the experiments. Spectroscopic measurements at fast acquisition rates showed both an increase in the intensity of the overall spectral emission and the growth of lines corresponding to ionic aluminum species taking place right before the occurrence of weld defects.

Remote sensing instrument for solid samples based on open-path atomic emission spectrometry

Design considerations and development steps towards the construction of an open-path laser-induced plasma spectrometer for remote elemental measurements are presented and the main variables influencing the analytical signal discussed. The instrument is based on a coaxial optical design where the interrogating laser beam and the returning plasma light share the same optical axis. This scheme allows both tight focusing of the infrared laser radiation to induce a plasma on a remote sample surface and collection of the ultraviolet-visible plasma emission through the same open air path. The selection of the optical scheme and the different components of the instrument are discussed on the basis of the measurement range, the light throughput and signal-to-noise ratio considerations. The results presented demonstrate the feasibility of the open-path laser-induced plasma spectrometry approach to remote atomic-emission spectrometry in the hundred meters range. Based on these results, additional estimations evidenc...

Development of a portable laser-induced plasma spectrometer with fully-automated operation and quantitative analysis capabilities

The development of a fully-automated portable LIPS instrument is described. The system integrates a 50 mJ per pulse Nd:YAG laser operating at 1064 nm, a 1/8 m spectrograph, an iCCD detector with computer controlled instrument operation, data acquisition and processing. A hand-held probe specially designed to provide sampling stability and ease of handling in field operations contains the laser head and the focusing and collection optics. Plasma light is guided to the main unit via a fiber optic cable. Results obtained in the field for steel scrap sorting are discussed regarding the analytical precision, accuracy, speed of analysis and sample variability. Additionally, the results are compared to those obtained by XRF at the laboratory, showing good correlation.