Javier Laserna

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...

Line-focused laser ablation for depth-profiling analysis of coated and layered materials

The performance features of line-focused laser ablation for the characterization of interfaces in layered materials by laser-induced plasma spectrometry (LIPS) have been compared with the point-focusing method in terms of signal precision, signal-to-noise ratio, ablation rates, and surface sensitivity. In both optical configurations a pulsed Nd:YAG laser beam operating at 532 nm, with a homogeneous energy distribution (flattop laser), is used to generate point and microline plasmas on the sample surface. Subsequent light from the plasma is spectrally resolved and detected with an imaging spectrograph and an intensified charge-coupled-device detector that is binned along the slit-height direction. Line-focusing LIPS permits much higher laser power input while maintaining relatively low laser fluence, thus yielding better surface sensitivity and improved detection power. Values of the signal-to-noise ratio are improved by a factor of 6. In addition the ablation rate is 9 nm/pulse with the microline approach compared with 23 nm/pulse obtained with the point-focusing method. The results demonstrate that the microline-focusing approach is suitable for the depth analysis of coated and layered materials.

Multielemental analysis of prehistoric animal teeth by laser-induced breakdown spectroscopy and laser ablation inductively coupled plasma mass spectrometry

Laser-induced breakdown spectroscopy (LIBS) and laser ablation (LA) inductively coupled plasma (ICP) mass spectrometry (MS) were utilized for microspatial analyses of a prehistoric bear (Ursus arctos) tooth dentine. The distribution of selected trace elements (Sr, Ba, Fe) was measured on a 26 mm×15 mm large and 3 mm thick transverse cross section of a canine tooth. The Na and Mg content together with the distribution of matrix elements (Ca, P) was also monitored within this area. The depth of the LIBS craters was measured with an optical profilometer. As shown, both LIBS and LA-ICP-MS can be successfully used for the fast, spatially resolved analysis of prehistoric teeth samples. In addition to microchemical analysis, the sample hardness was calculated using LIBS plasma ionic-to-atomic line intensity ratios of Mg (or Ca). To validate the sample hardness calculations, the hardness was also measured with a Vickers microhardness tester.

Spectral analysis of the acoustic emission of laser-produced plasmas

A Q-switched frequency Nd:YAG laser was focused on copper, aluminum, and lead targets. The acoustic emission accompanying plasma formation was acquired and analyzed in both the time and the frequency domains. Spectral analysis of the shock wave has proved to be a simple and low-cost diagnostic of plasma phenomena. In the time domain, several propagation mechanisms of the shock wave were observed and the velocity profile of the shock wave estimated. Spectral measurements were performed in the acoustic propagation regime of the shock waves. Spectral features related to the plasma formation mechanism were identified and discussed for copper, aluminum, and lead on the basis of the physical properties of these elements, the expansion mechanisms of the plasma, and an empirical parameter representative of the transported energy.

Deep Ablation and Depth Profiling by Laser-Induced Breakdown Spectroscopy (LIBS) Employing Multi-Pulse Laser Excitation: Application to Galvanized Steel

The potential of a multi-pulse (MP) laser excitation scheme for deep stratigraphy of electrolytically galvanized steel using laser-induced breakdown spectrometry (LIBS) has been evaluated. For this purpose, a commercial electro-optically (EO) Q-switched Nd:YAG laser was employed, where by reducing the delay between the Q-switch opening and the flash lamp, a train of pulses (up to 11) separated by approximately 7.40 μs was generated during one lamp flashing. Plasma emission after each individual laser pulse of the MP sequence was detected by a spectrograph equipped with an intensified charge-coupled device (iCCD) detector. With MP excitation, the ablation efficiency was increased tenfold on iron sample and 22.5-fold on zinc material with respect to dual-pulse or single-pulse excitation. The LIBS signal generated by MP excitation shows an analogous enhancement. Although the total energy per shot delivered to samples was only 60 mJ, it was possible using LIBS to measure the sample stratigraphy up to depths of 90 lm on zinc-coated steel sheets. A satisfactory agreement between the Zn thickness determined by the MP-LIBS system and data from the manufacturer has also been obtained.

Effect of Pulse Duration in Multi-Pulse Excitation of Silicon in Laser-Induced Breakdown Spectroscopy (LIBS)

The aim of this study is to investigate the mechanisms responsible for the increase in ablated mass and signal enhancement observed on multi-pulse excitation. Several experiments were designed to obtain evidence that confirms the laser–sample and/or laser–plasma interaction, with special attention to the role of the pulse width on these effects. A train of pulses, with a separation of a few microseconds between pulses, was used for laser-induced breakdown spectroscopy (LIBS) analysis. The signal emission of Si was improved by an enhancement factor of about 60 compared to conventional single-pulse LIBS (SP-LIBS). The number of spikes, their amplitude, and their pulse duration were found to be variable for different Q-switch delays. A temporal study was performed to determine whether or not a laser–plasma interaction took place. The effect of pulse width (as responsible of laser–sample interaction) was also evaluated. The results demonstrate that, although both interactions contribute to the observed effect, the process is predominantly governed by the pulse width.

Optical restriction of plasma emission light for nanometric sampling depth and depth profiling of multilayered metal samples.

Improvement in depth profiling capabilities of laser-induced breakdown spectrometry (LIBS) for multilayered samples has been attempted. For this purpose, in a typical LIBS experiment, an optical restriction consisting of a pinhole placed between the dichroic mirror and the collecting lenses has been used. This new optical approach allows observing only the light emission coming from the central region of the plume. The microplasma was created on the sample by a pulsed Nd:YAG laser operating at 1064 nm with a homogeneous distribution of energy across the beam. Light emitted by the microplasma was detected with an intensified charge-coupled device (iCCD) multichannel detector. The effect of pinhole diameter and the delay time influence on depth analysis have been assessed. An ablation range of only a few nanometers per pulse has been achieved. Depth profiles of various metals (Cr, Ni, Cu) from multilayered samples have been generated by LIBS and depth resolution at different delay times using various pinhole diameters have been calculated and compared.