Search

The aim of this study was to develop a novel biodegradable magnesium (Mg) alloy for bone implant applications. We used scandium (Sc; 2 wt %) and strontium (Sr; 2 wt %) as alloying elements due to their high biocompatibility, antibacterial efficacy, osteogenesis, and protective effects against corrosion. In the present work, we also examined the effect of a heat treatment process on the properties of the Mg-Sc-Sr alloy. Alloys were manufactured using a metal casting process followed by heat treatment. The microstructure, corrosion, mechanical properties, antibacterial activity, and osteogenic activity of the alloy were assessed in vitro. The results showed that the incorporation of Sc and Sr elements controlled the corrosion, reduced the hydrogen generation, and enhanced mechanical properties. Furthermore, alloying with Sc and Sr demonstrated a significantly enhanced antibacterial activity and decreased biofilm formation compared to control Mg. Also, culturing Mg-Sc-Sr alloy with human bone marrow-derived mesenchymal stromal cells showed a high degree of biocompatibility (90% live cells) and a significant increase in osteoblastic differentiation in vitro shown by Alizarin red staining and alkaline phosphatase activity. Based on these results, the Mg-Sc-Sr alloy heat-treated at 400°C displayed optimal mechanical properties, corrosion rate, antibacterial efficacy, and osteoinductivity. These characteristics make the Mg-Sc-Sr alloy a promising candidate for biodegradable orthopedic implants in the fixation of bone fractures such as bone plate-screws or intramedullary nails.

Tire evidence is a form of trace evidence that is often overlooked in today's forensics, while frequently found at crime or accident scenes, usually in the form of skid marks. The pattern of the tire skid mark has been used before to link a tire or car to a scene, but the widespread use of anti-lock braking systems makes this an almost impossible and abandoned route of analysis. With this in mind, using the chemical profile of a tire has potential to link a car or tire back to a scene in which its trace material is found. This study shows the successful use of the elemental profile of tire rubber to classify 32 different samples using laser-induced breakdown spectroscopy, analyzed by principal component analysis combined with linear discriminant analysis. A classification accuracy close to 99% shows the ever-growing use of laser-induced breakdown spectroscopy as a technique of choice for forensic analysis of tire rubber, opening the path for its use as a forensic evidence.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and laser-induced breakdown spectroscopy (LIBS) are widely accepted techniques for direct sampling of biological materials for elemental analysis, with increasing applications being reported over the recent years. This review is focused on the calibration materials used to quantify trace elements in different biological samples such as soft tissues (for instance brain, liver, hair) and hard tissues (bones and teeth). The design of a correct calibration strategy relies on the choice of an adapted reference material that can be commercially available or prepared in-house, which will be reviewed here. A large variety of methods has been approached and considered promising over the years, and the development of matrix-matched reference biological materials seems now closer than ever and gives hope to even better quantitation using LIBS and LA-ICP-MS.

Line broadening due to plasma processes or the instrument degrade spectral resolution leading to uncertainty in the elemental profile obtained by optical emission spectroscopy. A novel approach to quantify spectral interferences in laser-induced breakdown spectroscopy (LIBS) is introduced. This algorithm establishes a statistical interference factor (SIF) to quantify spectral interferences for individual line assignment in LIBS while using the full information provided by a spectrum. This factor combines fundamentals of plasma emission with a Bayesian analysis of the experimental spectrum using eventual prior knowledge about the sample and/or the conditions of analysis. Two types of prior knowledge were used to interpret spectra from a pure silicon sample as well as a NIST SRM 610 glass sample and alumina with a controlled Ni contamination at different concentrations. Knowledge of the elemental composition confirmed the existence of spectral lines with high sensitivity to interference while other lines are more appropriate for analysis due to their consistent SIFs despite having knowledge of the composition.

The quantification of elemental impurities in aluminum oxide powder is important due to its large demand for various industrial applications. One of the techniques to perform such analysis is Laser-Induced Breakdown Spectroscopy (LIBS) and to that end, powders are usually pressed into pellets. However, the density of the powder-compact is often not reported and its effect on the analytical figure-of-merit is unknown. In this work, we study the influence of aluminum oxide powder-compacts density of these pellets on the calibration curve of nickel contaminant. Our results show that the sensitivity increases whenthe grain size increases for a given density and that its relative standard deviation decreases with the density of the powder compacts without any grain size effect. These results imply that both the powder-compact density and the ultimate particle size of the powders must be specified in the protocol for building the calibration curve.

The controlled interaction of two high intensity beams opens new degrees of freedom for manipulating electromagnetic waves in air. The growing number of applications for laser filaments requires fine control of their formation and propagation. We demonstrate, experimentally and theoretically, that the attraction and fusion of two parallel ultrashort beams with initial powers below the critical value (70% Pcritical), in the regime where the non-linear optical characteristics of the medium become dominant, enable the eventual formation of a filament downstream. Filament formation is delayed to a predetermined distance in space, defined by the initial separation between the centroids, while still enabling filaments with controllable properties as if formed from a single above-critical power beam. This is confirmed by experimental and theoretical evidence of filament formation such as the individual beam profiles and the supercontinuum emission spectra associated with this interaction.

Laser-induced breakdown spectroscopy (LIBS) has recently demonstrated its unrivaled performance for broadband elemental imaging of surfaces. The dimensions of the laser sampling spot still being potentially larger than the interfaces of chemical domains, the plasma created at each location can be largely varying and inhomogeneous with contributions from the different sides of the interface. This variation can become problematic when imaging it on fiber bundles connected to multiple spectrometers. A spatially heterogeneous signal would lead to spatially dependent image on the fiber bundle causing inconsistent readings and loss of efficiency. Köhler illumination is used in this study to create a homogenous illumination, regardless of the source homogeneity, thus improving light collection efficiency. The performance of this approach was demonstrated with inhomogeneous spectral sources and applied to the LIBS analysis of a metallic interface, showing up to a sixfold improvement of the homogeneity of the plasma collection.

We present the design, performance, and initial activation of the Mobile Ultrafast High Energy Laser Facility, a 5 TW near-infrared laser source located on a multi-km test range at Kennedy Space Center. The system is compact, readily transportable, and provides a robust, tunable output suitable for long range studies of high intensity laser propagation. The supporting testing infrastructure, which includes stand-alone beam diagnostic stations and atmospheric monitoring capabilities, makes this facility ideal for the development of stand-off high energy ultrafast applications and fundamental studies of atmospheric laser science.

Forensic palynology has played a crucial role in many criminal investigations, from burglary to homicide, rape, war crimes, terrorism, and drug trafficking. With the emergence of DNA barcoding, pollen genomics has immense potential to classify and identify pollen taxonomically from its genetic signature. In forensic analysis, a non-destructive method for evidence is essential. Thus, several challenges exist for the extraction of DNA from the pollen grains, such as keeping the grain intact for secondary analysis and bypassing the issue of DNA mixtures more likely to be observed in a pollen assemblage. In this study, a new method was developed to address these challenges and was designed to extract genetic material while not destroying the pollen grain on a single grain level. We demonstrate the mehod's efficiency with Pinus echinata, Taxodium distichum, and Plantago lanceolata single pollen grains. Quantitative PCR amplification of two genetic markers, ribulose bisphosphate carboxylase (rbcL) and internal transcribed spacer 2 (ITS2), and digital microscopy demonstrates the non-destructive nature of this novel DNA extraction method from single pollen grains.

The effect of silica on the densification of transparent YAG ceramics has long been investigated. The present paper makes a step forward on the quantification of the Si amount in YAG. The study shows how to measure with a high level of accuracy the silicon concentration in YAG in different steps of the fabrication process. The Laser-Induced Breakdown Spectroscopy (LIBS) has been used to quantify the amount of silicon in a set of samples with 0–0.275 wt% silica. Nanometric silica soot or its precursor, TEOS, has been used as silica source. The analysis shows that more than 80 wt % of SiO2 evaporates during reactive-sintering under vacuum, most probably because SiO gas forms during sintering under low oxygen partial pressure. In-depth concentration maps were obtained by laser drilling with LIBS pulses. The results show the possibility to modify the amount of residual Si in YAG ceramics by adjusting the sintering and annealing process.

The quantification of silicon content during the reaction sintering preparation process was studied using Laser-Induced Breakdown Spectroscopy (LIBS). YAG ceramics with different additions of silica have been analyzed at different steps of the process, and a significant drop in silica content was observed after the vacuum sintering step, which can be attributed to evaporation. 1. Introduction It is well known that silica can be used as a sintering aid in yttrium aluminum garnet (YAG) ceramics, leading to transparency. This approach has been successfully used in the 1990s with colloidal silica and TEOS and has brought many interesting results since. However, even though there are various publications dealing with the effect of silica addition on the transparency and microstructure of YAG ceramics [1-4], the number of studies on the solubility of Si in YAG and the processes occurring during the ceramics production is limited. Recently, it was shown that Laser-Induced Breakdown Spectroscopy (LIBS) can be used for the quantitative determination of the variations in stoichiometry of YAG [5] and of the amount of silica [6]. The presentation shows an analysis of the amount and distribution of silicon in YAG ceramics at different steps of the production process using reactive sintering using Laser-Induced Breakdown Spectroscopy. Monitoring the Si content step by step provides important information about the reproducibility and consistency of the fabrication process, crucial for any further optimization. 2. Experimental A set of mixtures with different silicon content was prepared from oxide powders and TEOS or SiO2. The powders were mixed, granulated, pressed, treated in air, sintered under high vacuum and annealed in air. The silicon content was characterized by Laser-Induced Breakdown Spectroscopy (LIBS) at different steps of the preparation process, collecting data from multiple shots for each measurement (see Fig. 1). For selected samples, in-depth concentration maps were obtained. 3. Results After a calibration using stoichiometric mixtures of oxides, quantitative data for samples with the addition of TEOS ranging from 0 to 1 wt% were obtained. The obtained quantification limit was 0.0463 wt.% of SiO2 (216 ppm of Si). The most important change throughout the preparation process was observed with the vacuum sintering step, where a large part of silica left the material. A variation in the silicon content inside the samples was observed, with lower concentrations at the outer parts. 4. Conclusions The analysis of silicon content in YAG ceramics with different initial additions of silica provided a clear indication of a significant drop in silicon content after the vacuum sintering step, which can be attributed to evaporation. The presented results show that LIBS offers a user-friendly solution to a better understanding of the role and behavior of sintering additives in the processing of advanced ceramics. 5. References [1] Boulesteix R., Maître A., Baumard J.-F., Sallé C., Rabinovitch Y. Opt. Mater. 31 (2009) 711-715. [2] Stevenson A. J., Li X., Martinez M. A., Anderson J. A., Suchy D. L., Kupp E. R., Dickey E. C., Mueller K. T., Messing G. L., ,,Effect of SiO2 on densification and microstructure development in Nd:YAG Transparent Ceramics," J. Am. Ceram. Soc. 94 (2011) 1380-1387. [3] J. Hosta?a, L. Esposito, A. Piancastelli, "Influence of Yb and Si content on the sintering and phase changes of Yb:YAG laser ceramics," J. Eur. Ceram. Soc 32(11), 2949-2956 (2012). [4] R. Gaume., Y. He , A. Markosyan, R. L. Byer, "Effect of Si-induced defects on 1 µm absorption losses in laser-grade YAG ceramics," J. Appl. Phys. 111(9), 093104 1-5 (2012). [5] S. J. Pandey, M. Martinez, F. Pelascini, V. Motto-Ros, M. Baudelet, R. M. Gaume, "Quantification of non-stoichiometry in YAG ceramics using laser-induced breakdown spectroscopy," Opt. Mater. Express 7(2), 627-632 (2017). [6] S. J. Pandey, M. Martinez, J. Hosta?a, L. Esposito, M. Baudelet, R. Gaume, "Quantification of SiO2 sintering additive in YAG transparent ceramics by laser-induced breakdown spectroscopy (LIBS)," Opt. Mater. Express 7(5), 1666-1671 (2017). 5. Acknowledgements Romain Gaume wishes to thank the Air Force Office of Scientific Research for supporting his work under award number FA9550-18-1-0103.

The filament plasma resulting from the interaction between two co-propagating beams, separated by 180 and 280 µm, was characterized for different energy distributions – two subcritical beams, one subcritical beam with one filament, and two filaments.

High-power femtosecond filaments—laser-light beams capable of kilometer-long propagation—attract interest of nonlinear-optics community due to their numerous applications in remote sensing, lightning protection, virtual antennas, and waveguiding. Specific arrangements of filaments, into waveguides or hyperbolic metamaterials, allow for efficient control and guiding of electromagnetic radiation, radar-beam manipulation, and resolution enhancement. These applications require spatially uniform distribution of densely packed filaments. In order to address this challenge, we investigate the dynamic properties of large rectangular filament arrays propagating in air depending on four parameters: the phase difference between the neighboring beams, the size of the array, separation between the beams, and excitation power. We demonstrate that, as a result of the mutual interaction between the filaments, the arrays where the nearest neighbor beams are out-of-phase are more robust than the arrays with all the beams in phase. Our analysis of the array stability reveals that there exist certain trade-offs between the stability of a single filament and the stability of the entire array. We show that in the design of the experiment, the input parameters have to be chosen in such a way that they ensure a sufficiently high filling fraction, but caution has to be used in order not to compromise the overall array stability. In addition, we show the possibility of filament formation by combining multiple beams with energies below the filamentation threshold. This approach offers additional control over filament formation and allows one to avoid the surface damage of external optics used for filamentation.

Zinc is an element required in multiple biochemical processes in the human body as a structural, regulatory or catalytic ion. Its deficiency is linked to issues of a variety of health processes such as physical growth, immune system, or reproductive functions to name a few. Its quantitative determination using Laser-Induced Breakdown Spectroscopy (LIBS) on fingernails as a proxy has been proposed by many studies. In this study, a solid matrix-matched material was developed as a reference material for this type of analysis. A solution of alginic acid and keratin, spiked with zinc oxide nanoparticles, was cross-linked and dried to obtain a hard film. The calibration curve showed a determination coefficient of 0.986, Zn limit of detection of 13 μg.g−1 and limit of quantitation of 27 μg.g−1. The calibration curve was used on two toenails and the Zn concentration was confirmed by bulk ICP-MS. These results confirmed the potential for LIBS to be used for the quantitative diagnostic of Zn in fingernails using these adapted matrix-matched reference materials.

Laser ablation has become the most accepted method for direct sampling of solid materials, as in elemental trace analysis by laser-induced breakdown spectroscopy. However, the scarcity of matrix-matched standards or reference materials (such as NIST reference materials for instance) is an obstacle to quantitative analysis, particularly in the area of hard biological materials analysis, such as bones and teeth. If existing, the corresponding certified standards often consist of powders, then compacted as pellets which density, cohesive strength and dopant incorporation are not always representative of the samples under investigation, thereby casting serious uncertainties on calibration protocols. Here, we report on the synthesis of hydroxyapatite reference ceramic materials that can be doped controllably with various elements of interest. The fabrication process involves spiking during synthesis, prior to a hard sintering of pelletized ceramics. As a result, these materials have good chemical homogeneity and ablation properties that mimic those of naturally calcified biological tissues.

ZnMgO thin films were grown by Molecular Beam Epitaxy on closely-lattice-matched MgO substrates with a Radio-Frequency (RF) generated oxygen plasma. The impact on the cubic ZnMgO of oxygen flow rate and applied RF power was investigated under a high vacuum condition (1E-6 Torr). Optical Emission Spectroscopy identified active species in the plasma including O, O + , and O þ 2 . The emission intensity of these species was compared at oxygen flow rates ranging from 0.5 sccm to 2.5 sccm and applied RF powers from 150 W to 500 W. Plasma composition at operating conditions was determined by correlating changes in optical emission to changes in relative concentration of active species in the plasma. Atomic Force Microscopy and profilometry characterized changes in surface roughness and growth rate of produced films. Independently increasing flow rate and RF power increased growth rate while simultaneously decreasing roughness. Growth rate enhancement of 80% was achieved with an improvement in surface roughness from 7.5 nm to 3.3 nm in a 1 lm square. Optimal conditions are discussed for ZnMgO thin film epitaxy. 2013 Published by Elsevier B.V.

Transparent ceramics are important optical materials with applications in street lighting, high-strength windows, electro- and magneto-optical isolators, high-power laser gain media and radiation detectors. Their fabrication most often relies on powder densification techniques carried out at high temperatures, sometimes promoted by sintering additives. Here, we describe the application of laser-induced breakdown spectroscopy (LIBS) for following the concentration levels of silica used as a sintering agent in the fabrication of yttrium aluminum garnet (YAG) transparent ceramics. The sensitivity limit of our protocol reaches a few tens of ppm of silica in YAG ceramic samples, showing that LIBS can be implemented reliably for the rapid assessment of sintering additives in advanced ceramic processing.

Silica is typically used as a sintering aid in the production of transparent YAG (Y3Al5O12) ceramics, allowing for the achievement of nearly pore-free microstructures and the lowering of sintering temperatures. However, it was also found to introduce undesired color centers in the sintered material [1] as well as segregate at grain boundaries leading to the formation of amorphous or crystalline secondary phases (Y2SiO5) [2], which decrease the optical properties and compromise the use of the material as a laser medium. Thus, while the addition of silicon (in the form of SiO2 or as tetraethyl orthosilicate, TEOS) is often required, it is desirable to obtain materials with low Si content and homogeneous distribution. This work studies the amount of Si and its distribution in YAG and Yb:YAG ceramic materials produced by reaction sintering of a mixture of oxide powders throughout the whole preparation process. Monitoring the Si content step by step provides important information about the reproducibility and consistency of the fabrication process, crucial for any further optimization. We have shown that Laser-Induced Breakdown Spectroscopy (LIBS) allows sensitive and accurate quantification of silicon in ceramics down to 60 ppm and our experimental LIBS setup was used to analyze the evolution of the silicon content in samples at various steps of the fabrication process [3]. The distribution of Si in sintered ceramics was studied with High Resolution TEM to detect any possible nano-precipitates, and EDX nano-probe chemical analysis to check for segregation at grain boundaries and evaluate Si concentration within the YAG grains. The amount of Si present in the sintered materials has been found to be as low as 30 % of that introduced into the initial mixture. References 1. R. Gaume, Y. He, A. Markosyan and R.L. Byer, "Effect of Si-induced defects on 1 µm absorption losses in laser-grade YAG ceramics", J. Appl. Phys., 111, pp.093104, 2012 2. L. Esposito, T. Epicier, M. Serantoni, A. Piancastelli, D. Alderighi, A. Pirri, G. Toci, M. Vannini, S. Anghel and G. Boulon, "Integrated analysis of non-linear loss mechanisms in Yb:YAG ceramics for laser applications", J. Eur. Ceram. Soc., 32, pp.2273-2281, 2012 3. S.J. Pandey, M. Martinez, J. Hosta?a, L. Esposito, M. Baudelet and R. Gaume, "Quantification of SiO2 sintering additive in YAG transparent ceramics by Laser-Induced Breakdown Spectroscopy (LIBS)", Opt. Mater. Express (submitted)

White-Light LIDAR was performed using a unique polarization-controlled white light source generated by filamentation. The design and performance of this supercontinuum source will be shown as well as its importance for a novel LIDAR approach.

A method is described for performing discriminant analysis in the presence of interfering background signal. The method is based on performing target factor analysis on a data set comprised of contributions from analyte(s) and interfering components. A library of data from representative analyte classes is tested for possible contributing factors by performing oblique rotations of the principal factors to obtain the best match, in a least-squares sense, between test and predicted vectors. The degree of match between the test and predicted vectors is measured by the Pearson correlation coefficient, r, and the distribution of r for each class is determined. A Bayesian soft classifier is used to calculate the posterior probability based on the distributions of r for each class, which assist the analyst in assessing the presence of one or more analytes. The method is demonstrated by analyses performed on spectra obtained by laser induced breakdown spectroscopy (LIBS). Single and multiple bullet jacketing transfers to steel and porcelain substrates were analyzed to identify the jacketing materials. Additionally, the metal surrounding bullet holes was analyzed to identify the class of bullet jacketing that passed through a stainless steel plate. Of 36 single sample transfers, the copper jacketed (CJ) and non-jacketed (NJ) class on porcelain had an average posterior probability of the metal deposited on the substrate of 1.0. Metal jacketed (MJ) bullet transfers to steel and porcelain were not detected as successfully. Multiple transfers of CJ/NJ and CJ/MJ on the two substrates resulted in posterior probabilities that reflected the presence of both jacketing materials. The MJ/NJ transfers gave posterior probabilities that reflected the presence of the NJ material, but the MJ component was mistaken for CJ on steel, while non-zero probabilities were obtained for both CJ and MJ on porcelain. Jacketing transfer from a bullet to steel as the projectile passed through the steel also proved difficult to analyze. Over 50% of the samples left insufficient transfer to be identified. Transfer from NJ and CJ jacketing was successfully identified by posterior probabilities greater than 0.8.

The possibility of using Laser-Induced Breakdown Spectroscopy (LIBS) for measuring the moisture content of fresh food samples is studied. The normalized line emission of oxygen is highly correlated with the moisture content of the sample, cheese in our case, and can be used as a moisture marker in situations where oxygen interference from the matrix is not a critical issue. The linear correlation between the oxygen signal and the moisture content in the sample shows great potential for using LIBS as an alternative spectroscopic method for moisture monitoring.

Laser filament properties, including the plasma induced by the filamenting pulse in the medium, depend on the numerical aperture (NA) of the focusing optics used to create them. Recent studies of this dependence have revealed two distinct linear and non-linear filamentation regimes. High-resolution spatial and temporal electron density measurements are presented demonstrating the transition from the linear to nonlinear focusing regime. This study shows that the dominance of geometrical focusing in the linear (high NA) regime produces plasma with high peak densities and large plasma diameters, while filamentation in the nonlinear regime, equivalent to long distance filamentation, leads to low peak densities and small plasma diameters.

article i nfo Laser-induced breakdown spectroscopy Double pulse LIBS Laser ablation Laser heating Laser-induced particles Double-Pulse Laser-Induced Breakdown Spectroscopy of iron using both Nd:YAG and TEA-CO2 lasers has been investigated to better understand mechanisms of signal enhancement. The signal dependence on the delay between the two laser pulses shows an enhanced signal when the CO2 laser pulse interacts with the sample before the Nd:YAG pulse. Signal kinetics and a simple model of sample heating by the CO2 pulse show that the enhancement during the first 700 ns is due primarily to sample heating. Images of the sample surface after ablation as well as time-integrated pictures of the plasma suggest that particles are ejected from the surface during the first microseconds after the arrival of the CO2 pulse and provide fuel for the subsequent plasma created by the Nd:YAG laser.

In the nanosecond laser ablation regime, absorption of laser energy by the plasma during its early stage expansion critically influences the properties of the plasma and thus its interaction with ambient air. These influences can significantly alter spectral emission of the plasma. For organic samples especially, recombination of the plasma with the ambient air leads to interfering emissions with respect to emissions due to native species evaporated from the sample. Distinguishing interfering emissions due to ambient air represents a critical issue for the application of laser-induced breakdown spectroscopy (LIBS) to the analysis of organic materials. In this paper, we report observations of early stage expansion and interaction with ambient air of the plasma induced on a typical organic sample (nylon) using time-resolved shadowgraph. We compare, in the nanosecond ablation regime, plasmas induced by infrared (IR) laser pulses (1064 nm) and ultraviolet (UV) laser pulses (266 nm). Nanosecond ablation is compared with femtosecond ablation where the post-ablation interaction is absent. Subsequent to the early stage expansion, we observe for each studied ablation regime, spectral emission from CN, a typical radical for organic and biological samples. Time-resolved LIBS allows identifying emissions from native molecular species and those due to recombination with ambient air through their different time evolution behaviors.

This work experimentally demonstrates in air coupling between two beams below the critical power threshold for filamentation. Dependent upon the pulse overlap in space, time, and polarization these two beams are observed to fuse and form a single filament.

Experimental studies of laser induced filament propagation through atmospheric conditions have been done to understand the interaction of filaments with its propagating medium as they propagate at different pressures and through aerosols.

The propagation of near-infrared ultra-short laser pulses in the regime of anomalous dispersion of transparent solids is associated with a host of self-induced effects including a significant spectral broadening extending from the ultraviolet into the infrared region, pulse self-compression down to few-cycle pulse durations, free and driven third harmonic generation, conical emission and the formation of stable filaments over several \(\mathop{\mathrm{cm}}\nolimits\) showing the emergence of conical light bullets. We review measurements performed in different experimental conditions and results of numerical simulations of unidirectional propagation models showing that the interpretation of all these phenomena proceeds from the formation of non-spreading conical light bullets during filamentation.

Transparent ceramics are important optical materials with applications in street lightning, high-strength windows, electro- and magneto-optical isolators, high-power laser gain media and radiation detectors. Their fabrication most often relies on powder densification techniques carried out at high temperatures and promoted by dopants, so-called 'sintering additives'. The monitoring of sintering additive concentration, throughout the fabrication process of ceramics, is particularly important in optimizing their effect and maintaining high optical quality and consistency in these materials. Here, we describe the use of Laser-Induced Breakdown Spectroscopy (LIBS) for following the evolution of the concentration levels of silicon in the fabrication of YAG transparent ceramics, a well-known laser material. We have developed an adequate experimental protocol to measured silicon doping in the range of a few hundreds of ppm in test ceramic samples of YAG, and built a calibration curve to quantify it. These results show that LIBS can be reliably implemented for quick assessment of sintering aids in advanced ceramic processing. This work has been funded by the National Institute of Justice and the State of Florida.

Quantitative measurements of the angular distribution of the plasma line emission from a gallium arsenide (GaAs) target irradiated by a single laser-air filament are reported. These enable reliable estimates of the stand-off ranges possible with single-filament-induced laser-induced breakdown spectroscopy materials detection.

The analysis of the destruction and reformation of a single laser filament interacting with a single micro-sized water droplet allows a better understanding of filament propagation through atmospheric aerosols.

The microwave spectrum of o-chlorotoluene has been reinvestigated using molecular beam Fourier transform microwave (MB-FTMW) spectrometers in the frequency range of 4–23 GHz. Due to the high resolution of this molecular beam technique the analysis yielded improved rotational constants, centrifugal distortion constants, and, for the first time, the complete chlorine nuclear quadrupole coupling tensor. From the torsional fine structure the barrier to internal rotation of the methyl group was found to be 5.5798(52) kJ mol −1 . Experimental results and ab initio calculations are compared.

The transition between linear and nonlinear regimes of focusing for laser filamentation is described and shows the balance between plasma physics and nonlinear propagation for the stability of the laser filament and its properties.

Supercontinuum generation by filamentation in molecular gases is optimized by studying the ellipticity of the pulse polarization during the interaction with the species of the gas medium via strong field ionization and molecular alignment effects.

The analysis of the filament destruction and reformation as a single aerosol is positioned along the radial and longitudinal axes of the filament provides more understanding of the propagation of filaments in aerosol-containing media.

Laser filamentation in gases is often carried out in the laboratory with focusing optics to better stabilize the filament, whereas real-world applications of filaments frequently involve collimated or near-collimated beams. It is well documented that geometrical focusing can alter the properties of laser filaments and, consequently, a transition between a collimated and a strongly focused filament is expected. Nevertheless, this transition point has not been identified. Here, we propose an analytical method to determine the transition, and show that it corresponds to an actual shift in the balance of physical mechanisms governing filamentation. In high-NA conditions, filamentation is primarily governed by geometrical focusing and plasma effects, while the Kerr nonlinearity plays a more significant role as NA decreases. We find the transition between the two regimes to be relatively insensitive to the intrinsic laser parameters, and our analysis agrees well with a wide range of parameters found in published literature.

Sophora leaves from several areas in Beijing are analysed by femtosecond laser-induced breakdown spectroscopy (femto-LIBS). Although the used spectral detection system is not time-resolved, the spectral lines of trace mineral elements are detected and analysed. It is proven that the femto-LIBS can be an efficient method to detect mineral trace elements contained in tree leaves which is a biomonitor for atmospheric pollution assessment or botanic studies. An interesting case of correlation between trace elements detected in tree leaves and the pollution of the concerned area is presented, for the first time to our knowledge.

Polarization and supercontinuum generation are intimately intertwined, as our measurements of polarization evolution in filaments and supercontinuum spectrum demonstrate. Anomalous spectral broadening is observed for particular ellipticities in molecular gases, but not in rare gases.

Renewed interest in the properties and applications of air filaments produced by high intensity ultrafast lasers is being driven by new capabilities and fresh insight to the complex nonlinear phenomena occurring in filaments.

The design and construction of a compact 10 TW Ti:sapphire CPA system for the generation of filament arrays is presented. The design and implementation challenges are discussed, in particular the optimization of beam quality.

International audience; Terahertz-Radiation Enhanced Emission of Fluorescence (THz-REEF) was studied in the counter-propagating configuration as a more accurate representation of stand-off THz sensing scenarios. Determination of the THz amplitude and phase using this technique was successfully demonstrated.

International audience; Filamentation in the anomalous dispersion regime is experimentally shown to give rise to an extreme blueshifted continuum peak in the visible region even when the filament is formed by near-infrared pulses. Measurements and numerical simulations allow us to identify this peak as an axial component of the conical emission. Its features are characterized and quantitatively reproduced by the effective three-wave mixing model.

The overall objective of this MURI program is to obtain a comprehensive understanding of the interaction of ultrafast femtosecond laser pulses with matter, with specific reference to the detection of trace elements of materials by techniques such as LIBS and Raman spectroscopy. The UCF team forms the core effort for this MURI, and is concentrating on femtosecond (and nanosecond) LIBS interaction science, self-channeling of femtosecond laser radiation and standoff detection techniques, trace explosives detection, chemometrics and plasma modeling. The other members of the MURI bring key areas of expertise to the program. University of Nebraska, Lincoln (UNL-Dennis Alexander) in femtosecond LIBS, nanoparticles and fundamental interactions, University of California, Berkeley (UCB-Samuel Mao) in theory and experiments in the early stages of femtosecond laser materials interaction, Johns Hopkins University (JHU-Paul Dagdigian) in kinetics theory and LIBS spectroscopy, and Florida A&M University (FAMU-Lewis Johnson) in femtosecond and ns LIBS.

Utilizing the transparency of silicon at 2 μm, we are able to ablate the backside of 500-μm thick silicon wafers without causing any damage to the front surface using a novel nanosecond Tm:fiber laser system. We report on our high energy/high peak power nanosecond Tm:fiber laser and provide an initial description of the effects of laser parameters such as pulse duration and energy density on the ablation, and compare thresholds for front and backside machining. The ability to selectively machine the backside of silicon wafers without disturbing the front surface may lead to new processing techniques for advanced manufacturing in solar cell and microelectronics industries.

International audience; Strict control of composition is of paramount importance for the reproducible fabrication of advanced ceramics. In particular, the preparation of high-grade transparent ceramics of definite line-compounds requires that the ratio of major constitutive elements be quantified with a precision better than a fraction of a mole percent to prevent the precipitation of secondary phases and the scattering of light. Such a requirement poses difficult challenges to most analytical methods, especially when applied to nearly-stoichiometric insulating phases. In this work, we show that laser-induced breakdown spectroscopy (LIBS) is a well-suited technique for the assessment of non-stoichiometry in yttrium aluminum garnet (YAG) ceramics and that the aluminum to yttrium ratio can be determined with a resolution of 0.3 mol %, well within the phase boundaries of YAG.

Measurements and numerical simulations of the continuum created by laser filamentation in anomalous dispersion regime of fused silica allow us to identify the extreme blueshifted peak as an axial component of the conical emission.