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The present study describes the potential use of the Laser-induced breakdown spectroscopy (LIBS) coupled with the principle component analysis (PCA) for the discrimination/analysis of the precious gold alloy has been reported. It is very hard to discriminate between the Au-Alloys using conventional LIBS and it has been suggested that the use of multivariate methods assisted LIBS could solve the problem. Gold alloys of karats 18 K, 19 K, 20 K, 22 K, and 24 K with concentrations of 75, 79, 85, 93, and 99.9% have been tested and analyzed using LIBS. Plasma was generated on the surface of the target sample by focusing Nd: YAG laser under atmospheric pressure. Time-integrated emission spectra from plasma were collected in the range of 250–870 nm. The characteristic emission lines of constituents were identified using the NIST atomic spectra database. Normalized optical emission intensities of the detected elements were used as input data for principle component analysis (PCA). Five different three-dimensional clusters were observed, that belonged to five different karats of gold, suggesting the reliability of the model for the classification of precious alloy samples. The finding from this study showed that the LIBS coupled with PCA is an effective method for the classification of gold alloys with different percentages. [ABSTRACT FROM AUTHOR]

The paper discusses the results of studying the emission spectra and absolute radiation intensities of laser plasma generated by laser pulse on a xenon gas-jet target. A Nd:YAG laser, λ = 1064 nm, τ = 5.2 ns, Epulse = 0.8 J was used. The spectral range 3–20 nm was studied. Gas-jet targets were formed by a supersonic conical nozzle. Emission spectra of laser plasma were obtained and interpreted. Absolute radiation intensities were determined in a number of spectral bands under various conditions of gas-jet target excitation. [ABSTRACT FROM AUTHOR]

The paper considers the emission spectra and dependences of the emission intensity of a number of carbon lines in absolute units for laser plasma generated by laser pulse on CO2, CHF3, and CF4 gas jets on the gas pressure at the nozzle inlet. A pulsed Nd:YAG laser, λ = 1064 nm, τ = 5.2 ns, Eimp = 0.8 J was used. Gas-jet targets were formed by a supersonic conical nozzle, the pressure at the nozzle inlet varied in the range of 5–25 bar. The emission spectra of the investigated gases were compared and the reasons for the different dependences of the radiation intensity on the gas pressure at the nozzle inlet were analyzed. [ABSTRACT FROM AUTHOR]

We demonstrate the method of laser-induced plasma formation and characterization for achieving efficient high-order harmonics generation during the ablation of chromium and propagation of femtosecond pulses through the optimally adjusted plasma. The dynamics of chromium plasma spreading out from the target surface is correlated with the maximal harmonic yield for the non-resonant harmonics and resonance-enhanced harmonic. Plasma velocities at different regimes of ablation were correlated with the determination of the optimal delay between the heating pulses used for target ablation and femtosecond driving pulses propagating through this plasma. Laser-induced breakdown spectroscopy was used for the optimization of the fluency of heating pulses and determination of the parameters of plasma. The harmonics up to the forty order (in the case of 1300 nm driving pulses) and thirty order (in the case of 800 nm driving pulses) were obtained. The enhancement of the resonance-induced 29th harmonic of 800 nm radiation and 47th harmonic of 1300 nm radiation showed a direct relationship with the optimization of plasma characteristics. [ABSTRACT FROM AUTHOR]

In this work, conical cavities with a fixed top diameter and varied bottom diameter have been utilized to improve the signal intensity, signal-to-noise ratio (SNR), and signal stability of laser-induced breakdown spectroscopy (LIBS). It is observed that the postponement of the maximum enhancement of spectral intensity and SNR occurs abnormally with decreasing the bottom diameter due to the energy dissipation from the plasma to the cavity walls. Optimization of the cavity size indicates that the conical cavity is superior to the widely-used cylindrical cavity in improving the performance of LIBS. It is also found that the emission enhancement in the conical cavity with larger bottom diameters is attributed to the increase in plasma temperature and electron number density, but the enhancement in the conical cavity with smaller bottom diameters is ascribed to the growth of electron number density. For the first time, the exact efficiencies of conical cavities suppressing the total number density fluctuation are acquired to evaluate the performance of improving signal stability through analysis of the signal uncertainty composition. [ABSTRACT FROM AUTHOR]

The characteristic parameters as well as self-generated electric and magnetic fields of Nd:YAG laser (532 nm, 10 ns) ablated Al plasma have been measured by employing Langmuir, electric and magnetic probes, respectively. Plasma parameters such as electron temperature ( T e ) and electron number density ( n e ) as well as SGEMFs of Al plasma are measured as a function of laser irradiance ranging from 5.2 to 9.4 GW/cm2 at fixed probes to target distance of 10 mm. Both T e and n e of Al plasma show an increasing trend with the increase of laser irradiance and vary from 8 to 11 eV and 3.9 × 1014 to 7.07 × 1014/cm3, respectively. The SGEMFs show an overall increasing trend with the increase of laser irradiance and a decreasing trend with increasing probe to plume distances. The evaluated values of SGEMFs vary from 50 to 380 V/m and 89 to 165 G. The growth of SGEMFs has been explained on the basis of quadrupole distribution of charges at leading and trailing fronts of expanding plasma. By controlling plasma parameters such as electron temperature and electron density, laser generated plasmas can be efficiently used as sources of pulsed electric and magnetic fields in wake field accelerators. [ABSTRACT FROM AUTHOR]

Laser-produced plasmas of dual-pulse fiber-optic laser-induced breakdown spectroscopy with different target positions relative to the waist region of laser focusing are studied using fast imaging and optical emission spectroscopy (OES). The laser energy of the two laser pulses is both maintained at around 18 mJ (i.e. the total energy is 36 mJ). The inter-pulse delay is kept at 250 ns. Ten spot sizes changing from 947 to 543 μm are obtained by precisely adjusting the distance between the focusing lens and the target surface. The profile of laser beam output from fiber shows a distinct top-hat shape. When approaching the dual-pulse waist region, the self-absorption and self-reversal of matrix iron lines gradually become intense while the plasma emission is enhanced, but the signal-to-noise ratio of minor elements gradually decreases. Under a similar spot size, the emission intensity with the target surface behind the waist region is weaker than that in front of the waist region and also with greater jitters. The target surface position is optimized to deviate from the waist region by ~ 1.3–1.6 mm towards the focusing lens for improving SNR of minor elements, corresponding to the lens-to-sample distances of 11.8–12.1 mm. Plasma morphology has undergone a transformation from stream- to umbrella-like structure using the recorded Intensified Charge-Coupled Device (ICCD) images. The expansion distance of the plasma front is increased from 1.07 to 1.28 mm, and the plasma volume is increased from 0.59 to 1.60 mm3. Besides, by utilization of OES, the maximum variation of plasma temperature and line broadening width rise to 2702 K from 1630 and to 0.0492 from 0.0316 nm along the vertical direction. The significant increase of optical thickness and nonuniformity of plasma temperature and density is the main reason for the intensification of self-absorption. [ABSTRACT FROM AUTHOR]

The peak frequency of the terahertz radiation generated from the femtosecond laser-induced air plasmas is blue shifted with the increased second harmonics intensity when a high voltage is added upon the air plasmas. This blue shift is the result of the DC-biased field from the high voltage plus the AC-biased field from the second harmonics, indicating that this terahertz radiation frequency peak is tunable by varying the two field components. This tunable frequency peak is significant to various applications such as remote sensing and material characterization. [ABSTRACT FROM AUTHOR]

The control and arguably the tailoring aspect of technologies like pulsed laser deposition (PLD) rises from understanding the chemistry hidden by the laser generated plasma. With the continuous transition towards thin films with complex structures and geometries, the comprehension of the fundamental processes during the film deposition becomes critical. During the PLD of Mo and Eu-doped Lu2O3, optical emission spectroscopy was implemented for in-situ plasma monitoring. The spatial distribution of individual elements revealed the structuring of a stoichiometric plasma while the formation of LuO molecule within the plasma plume is seen as being induced by the addition of a minimum 1 Pa of O2. The energy of the ejected particles was controlled through doping and O2 pressure. The effect of O2 pressure over the plasma energy revealed a transition from an atomic dominated region towards a molecular dominated one. The properties of the resulted films were analyzed by XRD, AFM, and photoluminescence techniques and show a strong correlation between the dynamical regime of the plasma and their structural properties. [ABSTRACT FROM AUTHOR]

The period (∧ ) of nanograting in sapphire varied from 320 to 398 nm with increasing the laser fluence, which is similar to the change trend of period of the near-subwavelength ripples previously observed on the material surface ( 0.4 < ∧ / λ < 1 ) (Huang et al. in ACS Nano 3:4062, 2009). The result shows that the interference of the incident laser with the plasma could take place at the high-excited state of internal modified interface and leads to a spatial modulation of the local energy (fluence) distribution. The initial plasma–laser interference and the subsequent nanocrack-assisted plasma–laser coupling were used to explain the growth of nanograting what we have observed experimentally. Using a finite-difference time-domain method, we simulated the redistribution of laser fluence about the nanocracks, which derived from the pre-induced periodic refractive index changes in the focal volume after the acid etching. The experimental result and theoretical simulation can be in good agreement. In addition, we realized the erasing and rewriting of nanograting by using two beams of orthogonally polarized femtosecond laser pulses. This study can provide new proof for the physical mechanism of laser-induced nanograting and offer a reference for the fabrication of nanodevices in the substrate of sapphire. [ABSTRACT FROM AUTHOR]

In the present work, laser-induced plasma (LIP) of Mo is studied using both time and space resolved laser-induced breakdown spectroscopy (LIBS) in air as a function of incident laser energy. For this a second harmonic Q-switched Nd:YAG laser having pulse width of 7 ns and repetition rate of 1 Hz is used. The Boltzmann plot method is employed to estimate the plasma temperature of LIP using MoI and MoII lines separately. The stark-broadened profile of MoI-313.2 nm is exploited to measure the electron density. The temporal study in the time delay range of 0.5–5.0 μs shows that both the parameters, decay with the increase in delay time but increases with the increase in laser energy. It is observed that the plasma temperature estimated for MoII lines is higher than that of the MoI lines during the initial stage of plasma formation, delay time of 0.5–1.0 μs, but at a later time scale, both these species are found to possess nearly the same values of the temperature, indicating the coexistence of thermal equilibrium among the Mo atoms and ions in LIP. Therefore, in the second part of the experiment, time-integrated spatial evolution of the LIP of Mo is studied at a fixed delay of 2 μs as a function of axial distance normal to the target. It is found that emission intensity (MoI and MoII both), plasma temperature, and electron density initially increase with the increase in distance from the target, attains maximum value and then falls down. The Mc-Whirter criteria is applied to test the validity of local thermodynamic equilibrium (LTE). The relaxation time and diffusion length are estimated in time and space resolved studies respectively to take care of the transient and inhomogeneous nature of the LIP. The optical thin condition of LIP is verified by employing the branching ratio method. From these studies, a suitable spatio-temporal is identified where the LTE and optically thin plasma condition hold along with a high signal to noise ratio. [ABSTRACT FROM AUTHOR]

We demonstrate here, for the first time to the best of our knowledge, the method of classification and identification of metals, metal alloys using the color CCD images of femtosecond (fs) laser-induced plasma emissions. The non-gated color CCD images of the plasma emissions were used to train the machine learning algorithm for identification. We have also compared the obtained results with the fs-laser-induced breakdown spectroscopy (LIBS) results. The green channel in the RGB image was used for the classification and prediction of metals and metal alloys. The present work explores the possibility of identification of the aluminum, copper, bronze, and steel using a simple instrument such as the CCD. Each sample formed extended clusters in the classification performed using principal component analysis (PCA). The extracted features from the PCA were used as input to train the support vector machine (SVM) and for prediction and the results are intriguing. [ABSTRACT FROM AUTHOR]

In this paper, the quality assessment of isogams is demonstrated by laser-induced breakdown spectroscopy (LIBS) using the comparative standardization method. Here, the mass concentrations of carbon and hydrogen, as basic elements of tar, relative to that of calcium, as an undesired element, are taken into account as principal parameters to determine the quality of isogams. Hence, the intensity ratios of H α line of hydrogen (656.28 nm), the (0, 0) band of CN (388.34 nm), and the (0, 0) band of C2 (516.52 nm) to the line intensity of once-ionized calcium (317.93 nm) are considered as determinant markers for five different pre-known isogam brands. Qualitatively, classification of the isogams based on this approach is in full agreement with that obtained from the results of Fourier-transform infrared (FTIR) spectroscopy. In FTIR spectra, two stronger transitions of 2849 cm−1 and 2917 cm−1 related to the symmetric and asymmetric stretching vibrations of C–H play the principal role in the analysis of samples. Furthermore, the results obtained from energy-dispersive X-ray (EDX) analysis quantitatively confirm the LIBS outcomes. And finally, to reveal the differences between isogams from various aspects, the linear discriminant analysis (LDA) is exploited as a statistical approach. [ABSTRACT FROM AUTHOR]

The present work introduces a detailed investigation to discriminate between some types of igneous and sedimentary rocks. The used experimental setup was a conventional single-pulse nanosecond system with a neodymium YAG laser at two excitation wavelengths, 1064 nm, and 355 nm. The laser-induced emission spectra of the rock samples were normalized to the irradiance for both utilized laser wavelengths to compensate for the different laser pulse energies used. The surface hardness values of the studied samples were spectroscopically determined via the intensity ratios of the ionic-to-atomic spectral lines of iron in the rock samples. Besides, the laser-induced plasma parameters, namely the plasma temperature and the electron density, were calculated from the obtained spectral data. It is found that the plasma temperature, in the infrared-laser case, was higher than that of the ultraviolet laser while the electron density values were the opposite. Multivariate statistical analysis of the spectroscopic data using the principal component analysis technique revealed the possibility of discrimination between different types of rocks. Furthermore, the laser-induced breakdown spectroscopy results have been validated by comparison to the results of the energy-dispersive X-ray analysis for the same samples. [ABSTRACT FROM AUTHOR]

A hemispherical cavity can be used to improve the sensitivity of laser-induced breakdown spectroscopy by increasing the emission spectra of the plasma. In this work, laser-induced plasma plume images were obtained with and without confinement. The results have confirmed that the reason for the signal enhancement caused by the hemispherical cavity was the reflected shockwave "compressing" effect. The dependence of spectral signal enhancement on the material property of the cavities was investigated. Four cavities in different materials, which include K-resin, aluminum alloy, photosensitive resin and nylon, were used to confine the plasma. It has shown that the material physical properties of the cavities influence the enhancement effect. We found that the main influencing factor was surface roughness of the material. Smoother cavity surfaces induced stronger enhancement effects due to the larger specular reflection component of the reflected shockwave and the more intense subsequent interaction between the plasma and shockwave. The spectral intensities of the characteristic lines approximately doubled with surface roughness values changing from 0.2 to 16.1. [ABSTRACT FROM AUTHOR]

In this paper we report the investigation of the laser-induced breakdown and ignition behaviour of methane/air and dimethyl ether (DME)/air mixtures. Moreover, the optical emission from the induced plasma is utilized for determining the mixture composition quantitatively by means of laser-induced breakdown spectroscopy (LIBS). To the best of the authors' knowledge, LIBS and laser ignition of DME have not been reported in literature before. The technique under investigation is finally employed for combustion diagnostics in laminar as well as turbulent flames. In the laminar premixed and non-premixed flames the LIBS spectra allow spatially resolved measurements of the equivalence ratio and enable studying the mixing of gases provided through the burner with the surrounding room air. In addition, the breakdown threshold of the applied laser pulse energy yields an estimate for the local temperature. In the turbulent cases single-shot LIBS spectra are recorded at fixed position allowing the derivation of local statistical fluctuations of the equivalence ratio in partially premixed jet flames. The results show that laser-induced breakdowns have a strong potential for flame diagnostics and, under suitable conditions, for the ignition of combustible mixtures. [ABSTRACT FROM AUTHOR]

Oxide nanoparticles are widely studied because of their unique properties, including their crystalline phase, surface area, and porosity, which make them attractive for several applications. These properties are related to the increase in the surface/volume ratio when moving from the bulk to the nanoscale. For this reason, a diagnostic tool capable of monitoring the nanoparticle size and concentration during synthesis is particularly valuable. The laser-induced incandescence technique is widely used to provide such information. This study explored the applicability of this technique to TiO2 nanoparticles in flame spray synthesis. The fluorescence, flame emission, and incandescence signals were investigated. Time-resolved spectral measurements were first carried out on TiO2 nanoparticles deposited on a filter. At low laser fluences, the fluorescence signal of anatase TiO2 nanoparticles was detected. At higher fluences, the incandescence signal appeared. A fluence threshold limit that depended on the matrix effect was observed, above which breakdown phenomena occur. Then, laser-induced incandescence spectral measurements were performed on the flame spray at different heights above the burner and different acquisition delay times. The analysis showed the applicability and challenges in using this diagnostic tool in flame spray synthesis. [ABSTRACT FROM AUTHOR]

The main goal of this paper is to develop a distinct approach to laser-induced breakdown spectroscopy (LIBS) via internal reference standard (IRS) method with peak intensity-based self-absorption correction. On the other hand, since calcium amount of the body is determinant in the extent of osteoporosis, today, qualitative and quantitative analyses of plants rich in calcium is of particular importance. Hence, to evaluate the approach, calcium concentration of the leaf of five plants, fennel, bay leaf, dandelion, spinach, and parsley is determined using a special formulation which can be applied for four different combinations of neutral and once-ionized states of calcium as the analyte and copper as the IRS. The essential parameters of plasma including temperature and electron density, and eventually the calcium concentration are calculated for each leaf before and after correcting the self-absorption effect. Comparison of the results obtained from the method LIBS-IRS before correcting the self-absorption with those measured by inductively coupled plasma optical emission spectrometry indicates that, in determining the concentrations, there exist serious relative errors to the extent more than 189%; and this is while after correcting the self-absorption, the relative errors are reduced to the extent less than 2.8%. Accordingly, one can conclude that self-absorption correction using the peak intensity-based model surprisingly enhances accuracy of the method. [ABSTRACT FROM AUTHOR]

The purpose of the present study was to improve the detection limits of copper and lead in the soil samples by coupling Laser-Induced Plasma Spectrometry (LIPS) with an external magnetic field. The laser-induced plasma was generated using an Nd:YAG laser (532 nm) and the emission spectra were registered using a set of four spectrometers covering the wavelength region from 250 to 870 nm. The application of external magnetic field (0.7 T) perpendicular to the propagation of the plasma plume increases the plasma temperature, electron density, and plasma emission intensity. This enhancement in the plasma parameters is attributed to the plasma confinement. The detection limit of Pb and Cu has been improved from 12 ppm to 4.1 ppm and from 3.9 ppm to 1.4 ppm by applying magnetic field. The plasma temperature and electron number density decays slowly along the plasma expansion axis in the presence of external magnetic field. [ABSTRACT FROM AUTHOR]

The control and arguably the tailoring aspect of technologies like pulsed laser deposition (PLD) rises from understanding the chemistry hidden by the laser generated plasma. With the continuous transition towards thin films with complex structures and geometries, the comprehension of the fundamental processes during the film deposition becomes critical. During the PLD of Mo and Eu-doped Lu2O3, optical emission spectroscopy was implemented for in-situ plasma monitoring. The spatial distribution of individual elements revealed the structuring of a stoichiometric plasma while the formation of LuO molecule within the plasma plume is seen as being induced by the addition of a minimum 1 Pa of O2. The energy of the ejected particles was controlled through doping and O2 pressure. The effect of O2 pressure over the plasma energy revealed a transition from an atomic dominated region towards a molecular dominated one. The properties of the resulted films were analyzed by XRD, AFM, and photoluminescence techniques and show a strong correlation between the dynamical regime of the plasma and their structural properties. [ABSTRACT FROM AUTHOR]

Laser-induced breakdown spectroscopy (LIBS) has proven to be extremely versatile, providing multielement analysis in real time without sample preparation. The principle is based on the ablation of a small amount of target material by interaction of a strong laser beam with a solid target. The laser must have sufficient energy to excite atoms and to ionize them to produce plasma. We aimed to improve the LIBS limit of detection (LOD) and the precision of spectral lines emitted from the produced plasma by optimizing the parameters affecting the LIBS technique. LIBS LOD is affected by many experimental parameters such as interferences, self-absorption, spectral overlap, signal-to-noise ratio, and matrix effects. The plasma in the present study is generated by focusing a 6-ns pulsed Nd-YAG laser at the fundamental wavelength of 1,064 nm onto the Al target in air at atmospheric pressure. The emission spectra are recorded using an SE 200 Echelle spectrometer manufactured by the Catalina Corporation; it is equipped with an ICCD camera type Andor model iStar DH734-18. This spectrometer allows time-resolved spectral acquisition over the whole UV-NIR (200-1,000 nm) spectral range. Calibration curves for Cu, Mg, Mn, Si, Cr, and Fe were obtained with linear regression coefficients around 99 % on the average in aluminum standard alloy samples. The determined LOD has very useful improvements for Cu I at 521.85 nm, Si I at 288.15 nm, Mn I at 482.34 nm, and Cr I at 520.84 nm spectral lines. LOD is improved by 83.8 % for Cu, 49 % for Si, 84.3 % for Mn, and 45 % for Cr lower with respect to the previous works. [ABSTRACT FROM AUTHOR]

Dual-pulse laser-induced breakdown spectroscopy (LIBS) provides improved sensitivity compared to conventional single-pulse LIBS. We used a combination of Nd: yttrium aluminum garnet (YAG) and CO lasers to improve the sensitivity of LIBS. Significant emission intensity enhancement is noticed for both excited neutral lines and ionic lines for dual-pulse LIBS compared to single-pulse LIBS. However, the enhancement factor is found to be dependend on the energy levels of the lines, and resonance lines provided maximum enhancement. Our results indicate that IR reheating will cause significant improvement in sensitivity, regardless of the conditions, even with an unfocused reheating beam. The improved sensitivity with a YAG-CO laser combination is caused by the effective reheating of the pre-plume with a longer wavelength laser is due to efficient inverse Bremsstrahlung absorption. The role of the spot sizes, inter-pulse delay times, energies of the preheating and reheating pulses on the LIBS sensitivity improvements are discussed. [ABSTRACT FROM AUTHOR]