Femtosecond Laser-induced Breakdown Spectroscopy Research Articles

Generation of high-temperature and low-density plasma with strong spectral intensity by changing the distance between the focusing lens and target surface in femtosecond laser-induced breakdown spectroscopy

This paper exhibits the generation of high-temperature and low-density plasma with strong spectral intensity by changing the distance between focusing lens and target surface in femtosecond laser-induced breakdown spectroscopy.

Femtosecond laser-induced breakdown spectroscopy studies for the identification of plastics

We report the identification of five extensively used postconsumer plastics using the femtosecond laser-induced breakdown spectroscopy (fs-LIBS) technique.

基于纳秒和飞秒及双脉冲激光诱导击穿光谱的燃煤热值定量分析

基于纳秒和飞秒及双脉冲激光诱导击穿光谱的燃煤热值定量分析

Signal improvement using circular polarization for focused femtosecond laser-induced breakdown spectroscopy

The spectral intensity of plasma produced by focused femtosecond laser with circular polarization is higher than that with linear polarization.

Femtosecond double pulse laser-induced breakdown spectroscopy: Investigation of the intensity enhancement

Femtosecond laser-induced breakdown spectroscopy (fs LIBS) experiences a growing number of applications. We used a fs double pulse (DP) laser system to enhance the line intensities and we quantified the major mechanisms responsible for intensity enhancement in fs DP LIBS. The laser-induced plasma was excited by a 400 nm pulse and a delayed 800 nm pulse focused on metallic and oxide materials. The 400 nm pulses were produced by frequency doubling of the fundamental laser pulses at 800 nm. The laser radiation not converted by second harmonic generation was used as the 800 nm pulses. The LIBS spectra and the time-resolved plasma parameters were measured as function of pulse energies and correlated to the volume of ablation craters and the amount of nanoparticles formed in the process. Our results showed that the fs LIBS line intensities measured with double pulse excitation IDP were much higher than with single pulse excitation ISP. The intensity enhancement on metallic Cu was IDP/ISP = 2–30 depending on the energy of the first fs pulse. The dominating mechanisms of DP intensity enhancement were the increased number of atoms in plasma N and the higher plasma temperature T. The increase of N was due to the larger volume of DP ablation craters. The atomization of nanoparticles by laser-plasma-particle interaction contributed much less. The intensity enhancement was highest at lowest energy of the first pulse. Fs DP LIBS may thus enable elemental imaging with improved lateral resolution, higher sensitivity and increased elemental contrast.

Laser Spectroscopic Sensors for the Development of Anthropomorphic Robot Sensitivity.

The development of underwater robotics sensitivity, which is based on the sensors of laser spectroscopy methods, have been discussed. The ways to improve Laser Induced Fluorescence (LIF) and Laser Induced Breakdown Spectroscopy (LIBS) methods were investigated in order to develop and create laser sensitivity for underwater robotics. A brief overview is done in the article, where LIF and LIBS spectroscopy in underwater robotics are used as spectroscopy sensors in order to investigate underwater environments by means of underwater vehicles. Limit of Detection (LoD) of oil and oil product solutions in the seawater have been detected by means of nanosecond and femtosecond spectroscopy LIF. All results, which had been received by laser pulses of different duration, were compared. The same experiments have been provided in order to measure concentrations of elements in the seawater and solutions by the LIBS method. It was discovered that the LoD of a group of elements was reduced when the femtosecond LIBS was used. Anthropomorphic complexes were under discussion in order to adopt laser spectroscopy sensors for underwater environments. The submersible module, which was constructed to investigate and examine laser spectroscopy sensors, has been described.

Using LIBS to diagnose melanoma in biomedical fluids deposited on solid substrates: Limits of direct spectral analysis and capability of machine learning

Diagnosis is crucial to increase the success rate of cancer treatments as well as the survival rate and life quality of patients, in particular for forms of cancer that remain largely asymptomatic until metastasis. Methodologies that allow the diagnosis of early-stage tumors as well as the detection of residual disease have the potential to improve cancer control and help monitor therapeutic outcomes. In this work, we report a Laser-Induced Breakdown Spectroscopy (LIBS) approach to early diagnosis of a form of skin cancer, melanoma, based on the analysis of biological fluids (blood and tissue homogenates) harvested from diseased mice and healthy controls. We acquired femtosecond LIBS spectra and used two different approaches for the analysis: through comparison of the emission intensity of selected analytes in healthy and diseased samples; and by using machine learning classification algorithms (LDA, Linear Discriminant Analysis; FDA, Fisher Discriminant Analysis; SVM, Support Vector Machines; and Gradient Boosting). We also addressed the effect of substrates on the analysis of liquid samples, by using four different substrates (PVDF, Cu, Al, Si) and comparing their performance. We show that with a combination of the most appropriate substrate and algorithm, we are able to discriminate between healthy and diseased mice with accuracy up to 96% while direct analysis of LIBS spectra did not provide any conclusive results. These series of results demonstrate that carefully designed LIBS measurements combined with machine learning can be a powerful and practical approach for the diagnosis of cancer.

Femtosecond laser induced breakdown spectroscopy based standoff detection of explosives and discrimination using principal component analysis.

We report the standoff (up to ~2 m) and remote (~8.5 m) detection of novel high energy materials/explosive molecules (Nitroimidazoles and Nitropyrazoles) using the technique of femtosecond laser induced breakdown spectroscopy (LIBS). We utilized two different collection systems (a) ME-OCT-0007 (commercially available) and (b) Schmidt-Cassegrain telescope for these experiments. In conjunction with LIBS data, principal component analysis was employed to discriminate/classify the explosives and the obtained results in both configurations are compared. Different aspects influencing the LIBS signal strength at far distances such as fluence at target, efficiency of collection system etc. are discussed.

Influence of electron dynamics on the enhancement of double-pulse femtosecond laser-induced breakdown spectroscopy of fused silica

Femtosecond laser pulse train induced breakdown of fused silica was studied by investigating its plasma emission and the ablated crater morphology. It was demonstrated that the electron dynamics in the ablated fused silica play a dominant role in the emission intensity of induced plasma and the volume of material removal, corresponding to the evolution of free-electron, self-trapped excitons, and the phase change of the fused silica left over by the first pulse. For a fluence of 11 J/cm2, the maximum plasma intensity of double-pulse irradiation at an interpulse delay of 120 ps was about 35 times stronger than that of a single-pulse, while the ablated crater was reduced by 27% in volume. The ionization of slow plume component generated by the first pulse was found to be the main reason for the extremely high intensity enhancement for an interpulse delay of over 10 ps. The results serve as a route to simultaneously increase the spatial resolution and plasma intensity in laser-induced breakdown spectroscopy of dielectrics.

Femtosecond laser-ablation spark-induced breakdown spectroscopy and its application to the elemental analysis of aluminum alloys

A high repetition rate spark discharge was used to improve the analytical sensitivity of the conventional femtosecond laser-induced breakdown spectroscopy.

Spatial confinement effect on femtosecond laser-induced Cu plasma spectroscopy

The effect of spatial confinement on femtosecond laser-induced Cu plasmas was investigated by time-resolved spectroscopy. The cylindrical cavities with various diameters (2 and 3 mm) and various heights (2, 3, and 4 mm) were placed on the sample surface. An obvious enhancement in the emission intensity of Cu atomic lines was observed when a cylindrical cavity was used to confine the femtosecond laser-induced Cu plasmas. The results showed that enhancement ratios in femtosecond laser-induced breakdown spectroscopy with spatial confinement varied with cavity diameters and atomic emission lines selected. The spatial confinement effect was not significantly influenced by the cavity height because the height of plasma plume is lower than the cavity height. The maximum enhancement ratio for the emission intensities of the Cu atomic lines was measured to be around 3 at a time delay of 3.5 μs when the cavity diameter is 2 mm. The spectral enhancement is attributed to the compression of the plasma by the reflected shock wave.

Femtosecond laser-induced breakdown spectroscopy: Elemental imaging of thin films with high spatial resolution

We investigate femtosecond laser-induced breakdown spectroscopy (fs-LIBS) for the spectrochemical imaging of thin films with high spatial resolution. Chemical images are obtained by recording LIBS spectra at each site of 2D raster-scans across the samples employing one fs-laser pulse per site. The diffraction images of the Echelle spectrometer are binned to reduce the read-out time of the intensified CCD detector and to increase the stability of the emission signals against peak drifts in the echellograms. For copper thin films on glass the intensities of Cu I emission lines and the size of ablation craters vary non-monotonously with the film thickness hCu=5–500nm. The emission efficiency, defined as the Cu I line intensity per ablated volume, strongly decreases for films thicker than the optical penetration depth. The Na I line intensity from glass increases exponentially with decreasing Cu film thickness. For yttrium barium copper oxide (YBCO) thin films on MgO various atomic and molecular emission lines of the laser-induced plasma are measured (film thickness hYBCO=200–1000nm). The obtained element (Y, Ba, Cu, Mg) and molecular (Y-O) fs-LIBS images match the structure of the micro-patterned YBCO films very well. The achieved lateral resolution δr=6μm is among the best values reported for spectrochemical LIBS imaging.

Fs-laser ablation of teeth is temperature limited and provides information about the ablated components.

The goal of this work is to investigate the thermal effects of femtosecond laser (fs-laser) ablation for the removal of carious dental tissue. Additional studies identify different tooth tissues through femtosecond laser induced breakdown spectroscopy (fsLIBS) for the development of a feedback loop that could be utilized during ablation in a clinical setting. Scanning Election Microscope (SEM) images reveal that minimal morphological damages are incurred at repetition rates below the carbonization threshold of each tooth tissue. Thermal studies measure the temperature distribution and temperature decay during laser ablation and after laser cessation, and demonstrate that repetition rates at or below 10kHz with a laser fluence of 40 J/cm2 would inflict minimal thermal damage on the surrounding nerve tissues and provide acceptable clinical removal rates. Spectral analysis of the different tooth tissues is also conducted and differences between the visible wavelength fsLIBS spectra are evident, though more robust classification studies are needed for clinical translation. These results have initiated a set of precautionary recommendations that would enable the clinician to utilize femtosecond laser ablation for the removal of carious lesions while ensuring that the solidity and utility of the tooth remain intact.

Emission enhancement of femtosecond laser-induced breakdown spectroscopy by combining nanoparticle and dual-pulse on crystal SiO2

Metal nanoparticle deposition on sample surface is a promising approach to enhance the emission signal during laser-induced breakdown spectroscopy (LIBS). In this article, strong optical emission enhancement was achieved by combining nanoparticle enhanced LIBS (NELIBS) and double pulse LIBS (DP-LIBS) on a crystal SiO2 sample by using femtosecond laser. Thermal dewetting was used to deposit gold (Au) nanoparticles (NPs) on sample surface and NPs with different size were obtained by altering the thickness of the Au film. It was found that both the size and distribution of Au NPs significantly affected the enhancement effect of NELIBS and the Au NPs made from 7.5nm gold film had the best enhancement effect. The fundamental features of NELIBS enhancement for dielectric target were investigated by studying the photon absorption process. At a low laser fluence of 4.4J/cm2, an enhancement factor of about 13 for spectrum intensity was obtained in NELIBS and reached to 30 after being combined with DP-LIBS.

Rapid detection of drought stress in plants using femtosecond laser-induced breakdown spectroscopy.

Drought stress disrupts the balance of macro- and micronutrients and affects the yield of agriculturally and economically significant plants. Rapid detection of stress-induced changes of relative content of elements such as sodium (Na), potassium (K), calcium (Ca) and iron (Fe) in the field may allow farmers and crop growers to counter the effects of plant stress and to increase their crop return. Unfortunately, the analytical methods currently available are time-consuming, expensive and involve elaborate sample preparation such as acid digestion which hinders routine daily monitoring of crop health on a field scale. We report application of an alternative method for rapid detection of drought stress in plants using femtosecond laser-induced breakdown spectroscopy (LIBS). We demonstrate daily monitoring of relative content of Na, K, Ca and Fe in decorative indoor (gardenia) and cultivated outdoor (wheat) plant species under various degrees of drought stress. The observed differences in spectral and temporal responses indicate different mechanisms of drought resistance. We identify spectroscopic markers of drought stress which allow for distinguishing mild environmental and severe drought stress in wheat and may be used for remote field-scale estimation of plant stress resistance and health.

Interaction of femtosecond laser pulses with plants: towards distinguishing weeds and crops using plasma temperature

The ability to distinguish between crops and weeds using sensors from a distance will greatly benefit the farming community through improved and efficient scouting for weeds, reduced herbicide input costs and improved profitability. In the present study, we examined the utility of femtosecond laser-induced breakdown spectroscopy (LIBS) for plant species differentiation. Greenhouse-grown plants of dallisgrass, wheat, soybean and bell pepper were evaluated using LIBS under an ambient environment. LIBS experiments were performed on the leaf samples of different plant species using a femtosecond laser system with an inexpensive lightweight detector. Temperatures of laser-induced plasma in plants depend on many parameters and were determined for each of the study species by the constituent elements interacting with femtosecond laser pulses. Using elemental calcium transitions in plant tissue samples to measure plasma temperatures, we report consistent differences among the four study species, with average values ranging from 5090 ± 168 K (soybean) to 5647 ± 223 K (dallisgrass).

Mercury Amalgam Diffusion in Human Teeth Probed Using Femtosecond LIBS.

In this work the diffusion of mercury and other elements from amalgam tooth restorations through the surrounding dental tissue (dentin) was evaluated using femtosecond laser-induced breakdown spectroscopy (fs-LIBS). To achieve this, seven deciduous and eight permanent extracted human molar teeth with occlusal amalgam restorations were half-sectioned and analyzed using pulses from a femtosecond laser. The measurements were performed from the amalgam restoration along the amalgam/dentin interface to the apical direction. It was possible to observe the presence of metallic elements (silver, mercury, copper and tin) emission lines, as well as dental constituent ones, providing fingerprints of each material and comparable data for checking the consistence of the results. It was also shown that the elements penetration depth values in each tooth are usually similar and consistent, for both deciduous and permanent teeth, indicating that all the metals diffuse into the dentin by the same mechanism. We propose that this diffusion mechanism is mainly through liquid dragging inside the dentin tubules. The mercury diffused further in permanent teeth than in deciduous teeth, probably due to the longer diffusion times due to the age of the restorations. It was possible to conclude that the proposed femtosecond-LIBS system can detect the presence of metals in the dental tissue, among the tooth constituent elements, and map the distribution of endogenous and exogenous chemical elements, with a spatial resolution that can be brought under 100 µm.

Temperature effect on femtosecond laser-induced breakdown spectroscopy of glass sample

In this study, we observed the evolution of the spectral emission intensity of a glass sample with the increase of sample temperature, laser energy, and delay time in femtosecond laser-induced breakdown spectroscopy (fs-LIBS). In the experiment, the sample was uniformly heated from 22 °C to 200 °C, the laser energy was changed from 0.3 mJ to 1.8 mJ, and the delay time was adjusted from 0.6 μs to 3.0 μs. The results indicated that increasing the sample temperature could enhance the emission intensity and reduce the limits of detection, which is attributed to the increase in the ablated mass and the plasma temperature. And the spectral intensity increases with the increase of the laser energy and the delay time, however, the spectral line intensity no longer increases when the laser pulse energy and delay time reach a certain value. This study will lead to a further improvement in the applications of fs-LIBS.

Characterization of organic photovoltaic devices using femtosecond laser induced breakdown spectroscopy

The potential of laser induced breakdown spectroscopy (LIBS) as a non-contact probe, for characterizing organic photovoltaic devices during selective laser scribing, was investigated. Samples from organic solar cells were studied, which consisted of several layers of materials including a top electrode (Al, Mg or Mo), organic layer, bottom electrode (indium tin oxide), silicon nitride barrier layer and substrate layer situated from the top consecutively. The thickness of individual layers varies from 115 to 250nm. LIBS measurements were performed by use of a 40 femtosecond Ti:Sapphire laser operated at very low pulse energy (<10micro-joule) to ensure a fine depth-profiling of the very thin layers. Probing a fixed spot on the sample with successive laser pulses, produced plasma emission spectra corresponding to individual laser ablation events. This enabled discrimination of the different layers on the basis of characteristic spectral lines reflecting key elemental constituents of each layer in the organic solar cell structure, demonstrating the potential of LIBS for fast, non-contact characterization of organic photovoltaic coatings.

Re-Heating Effect on the Enhancement of Plasma Emission Generated from Fe Under Femtosecond Double-Pulse Laser Irradiation**supported by the National Basic Research Program of China (No. 2013CB922200), the China Postdoctoral Science Foundation (No. 2014M551169), National Natural Science Foundation of China (Nos. 11674128, 11474129 and 11504129)

In this paper, we present a study on the effect of inter-pulse delay using femtosecond double-pulse laser-induced breakdown spectroscopy in a collinear geometry. The temporal evolution of spectral intensity is performed for the lines of Fe I 423.60 nm, Fe I 425.08 nm and Fe I 427.18 nm. It is found that, by selecting appropriate inter-pulse delay, the signal enhancement can be significantly increased compared with the single-pulse case. A three-fold enhancement in the current experiment is obtained. The plasma temperature and electron density are also investigated based on the theory of Boltzmann plot and Stark broadening. We attribute the main mechanism for emission enhancement to the plasma re-heating effect.