Filament-induced Breakdown Spectroscopy Research Articles

Optimization of filament-induced breakdown spectroscopy of metal-containing water with deep reinforcement learning

Optimization of filament-induced breakdown spectroscopy of metal-containing water with deep reinforcement learning

Filament-induced breakdown spectroscopy of solids through highly scattering media.

Ultrafast laser pulse filamentation in the air can be used for remote sensing by exciting a characteristic optical emission, which is usually referred to as filamentation-induced breakdown spectroscopy. In environments that impede light propagation, such as fog, haze, or clouds, scattering makes it challenging to propagate laser beams and retrieve generated optical signatures. We demonstrate the effectiveness of laser filamentation for simultaneously clearing the path for intense femtosecond pulse propagation in a highly scattering medium, generation of luminous plasma on a solid target, and counter-propagation of a characteristic spectroscopic signal over a cleared channel along the filament path. In a dense cloud, the counter-propagating signal predominantly transits the cleared on-axis path but is highly affected by the negative thermal lensing of a Gaussian beam. These insights enhance our understanding of laser filamentation in atmospheric sensing and could substantially improve remote detection capabilities in poor visibility conditions.

Filament induced breakdown spectroscopy with enhanced excitations from plasma gratings

The interaction of two or three filaments generates a plasma grating, with a focus lens collecting the plasma emission into a spectrometer from the side direction after plasma grating ablating the sample.

Breakdown Spectroscopy Induced by Nonlinear Interactions of Femtosecond Laser Filaments and Multidimensional Plasma Gratings

Breakdown spectroscopy is a valuable tool for determining elements in solids, liquids, and gases. All materials in the breakdown region can be ionized and dissociated into highly excited fragments and emit characteristic fluorescence spectra. In this sense, the elemental composition of materials can be evaluated by detecting the fluorescence spectrum. This paper reviews the recent developments in laser-induced breakdown spectroscopy. The traditional laser-induced breakdown spectroscopy, filament-induced breakdown spectroscopy, plasma grating, and multidimensional plasma grating-induced breakdown spectroscopy are introduced. There are also some proposals for applications of plasma gratings, such as laser ablation, laser deposition, and laser catalysis of chemical reactions in conjunction with research on the properties of plasma gratings.

Sensing Trace-Level Metal Elements in Water Using Chirped Femtosecond Laser Pulses in the Filamentation Regime.

Femtosecond filament-induced breakdown spectroscopy (FIBS) is an efficient approach in remote and in situ detection of a variety of trace elements, but it was recently discovered that the FIBS of water is strongly dependent on the large-bandgap semiconductor property of water, making the FIBS signals sensitive to laser ionization mechanisms. Here, we show that the sensitivity of the FIBS technique in monitoring metal elements in water can be efficiently improved by using chirped femtosecond laser pulses, but an asymmetric enhancement of the FIBS intensity is observed for the negatively and positively chirped pulses. We attribute the asymmetric enhancement to their different ionization rates of water, in which the energy of the photons participating in the ionization process in the front part of the negatively chirped pulse is higher than that in the positively chirped pulse. By optimizing the pulse chirp, we show that the limit of detection of the FIBS technique for metal elements in water, e.g., aluminum, can reach to the sub-ppm level, which is about one order of magnitude better than that by the transform-limited pulse. We further examine the FIBS spectra of several representative water samples including commercial mineral water, tap water, and lake water taken from two different environmental zones, i.e., a national park and a downtown business district (Changchun, China), from which remarkably different concentrations of Ca, Na, and K elements of these samples are obtained. Our results provide a possibility of using FIBS for direct and fast metal elemental analysis of water in different field environments.

Dependence of the Intensity of Emission Lines of Chemical Elements on Laser Pulse Duration in the Method of Filament-Induced Breakdown Spectroscopy of Aqueous Aerosol

Dependence of the Intensity of Emission Lines of Chemical Elements on Laser Pulse Duration in the Method of Filament-Induced Breakdown Spectroscopy of Aqueous Aerosol

Propagation distance-resolved characteristics of copper plasma emission induced by axicon-focused femtosecond laser filamentation in air.

It is well known that Bessel beams have non-diffractive characteristics, which can be generated by Gaussian beams focused by an ideal axicon. In general, the length of filament generated by Bessel beams is longer than that by Gaussian beams and the electron density in the filament generated by Bessel beams is more uniform. This paper experimentally studied the propagation distance-resolved characteristics of copper plasma emission induced by axicon-focused femtosecond laser filamentation in the air. The evolution of the spectral intensity, plasma temperature, and electron density with the filament propagation path was obtained. The experiment results showed that when the base angle of the axicon was 5.0°, the spectral intensity along with the filament propagation path was more stable than that the base angle of the axicon was 0.5°. The changes in the plasma temperature and electron density along the filament propagation path were consistent with the change in the spectral intensity. This work provides a demonstration for the applications of filament-induced breakdown spectroscopy (FIBS), such as long-distance detection.

Dependence of the intensity of emission lines of chemical elements on the duration of laser pulses in the method of filament-induced breakdown spectroscopy of aqueous aerosol

Dependence of the intensity of emission lines of chemical elements on the duration of laser pulses in the method of filament-induced breakdown spectroscopy of aqueous aerosol

Laser-induced fluorescence of filament-produced plasmas

Self-guided ultrafast laser filaments are a promising method for laser beam delivery and plasma generation for standoff and remote detection of elements and isotopes via filament-induced breakdown spectroscopy (FIBS). Yet, there are several challenges associated with the practical application of FIBS, including delivery of sufficient laser energy at the target for generating plasma with a copious amount of emission signals for obtaining a high signal-to-noise ratio. Here, we use laser-induced fluorescence (LIF) to boost the emission signal and reduce self-reversal in the spectral profiles. Ultrafast laser filaments were used to produce plasmas from an Al 6061 alloy target at various standoff distances from 1 to 10 m. For LIF emission enhancement, a narrow linewidth continuous-wave laser was used in resonance with a 394.40 nm Al I resonant transition, and the emission signal was monitored from the directly coupled transition at 396.15 nm. Emission signal features of Al I are significantly enhanced by resonant excitation. In addition, LIF of filament ablation plumes reduces the self-reversal features seen in the thermally excited spectral profiles. Time-resolved two-dimensional fluorescence spectroscopy was performed for evaluating the optical saturation effects, which are found to be non-negligible due to high Al atomic densities in the filament-produced plasmas.

Effect of the target positions on the rapid identification of aluminum alloys by using filament-induced breakdown spectroscopy combined with machine learning

Filament-induced breakdown spectroscopy (FIBS) combined with machine learning algorithms was used to identify five aluminum alloys. To study the effect of the distance between focusing lens and target surface on the identification accuracy of aluminum alloys, principal component analysis (PCA) combined with support vector machine (SVM) and K-nearest neighbor (KNN) was used. The intensity and intensity ratio of fifteen lines of six elements (Fe, Si, Mg, Cu, Zn, and Mn) in the FIBS spectrum were selected. The distances between the focusing lens and the target surface in the pre-filament, filament, and post-filament were 958 mm, 976 mm, and 1000 mm, respectively. The source data set was fifteen spectral line intensity ratios, and the cumulative interpretation rates of PC1, PC2, and PC3 were 97.22%, 98.17%, and 95.31%, respectively. The first three PCs obtained by PCA were the input variables of SVM and KNN. The identification accuracy of the different positions of focusing lens and target surface was obtained, and the identification accuracy of SVM and KNN in the filament was 100% and 90%, respectively. The source data set of the filament was obtained by PCA for the first three PCs, which were randomly selected as the training set and test set of SVM and KNN in 3:2. The identification accuracy of SVM and KNN was 97.5% and 92.5%, respectively. The research results can provide a reference for the identification of aluminum alloys by FIBS.

Raising the saturation point of fluorescence emitted by air optical filament via π phase plate

Femtosecond laser filament induced breakdown spectroscopy is a promising technique that can be used in the remote sensing of air pollutants. Raising the laser energy saturation point below which the laser filament fluorescence increases exponentially with the incident laser energy will significantly improve the sensing sensitivity and detection distance. In this work, a saturation point raising scheme is proposed in which a quarter-circle π phase plate is used to form four optical filaments in air. The extrapolation based on the experimental results infers that the employment of the quarter-circle π phase plate and its induced multiple filaments can lead to the increase of the laser energy saturation point by four times, which is proportional to the number of sub-regions in the phase plate.

Limits of Detection of Chemical Elements in an Aqueous Aerosol in Filament-Induced Breakdown Spectroscopy

The capabilities of filament-induced breakdown spectroscopy for the analysis of the elemental composition of aqueous aerosols were estimated. The diameter of aqueous aerosol droplets in the atmosphere was 0.8–2.0 μm. The emission lines of the chemical elements were excited by fi lamentation of femtosecond laser pulses (60 fs, 800 nm, 4.4 mJ) in weak focusing mode by a lens with a focal length of 500 mm. The obtained limits of detection for Al (396.15 nm), Ba (553.35 nm), Ca (422.67 nm), Mg (285.21 nm), Na (588.99 nm), and Mn (403.08 nm) in an aqueous aerosol were 12.1, 41.7, 10.0, 7.3, 0.7, and 32.3 mg/L, respectively.

Filament-induced breakdown spectroscopy signal enhancement using optical wavefront control

Filament-induced breakdown spectroscopy (FIBS) is an analytical method that holds significant promise for remote sensing. In FIBS, it is desirable to maximize the intensity and improve the reproducibility of a selected spectroscopic feature. We demonstrate the use of wavefront control in conjunction with a genetic algorithm in FIBS of metallic copper and show that this approach can increase the efficacy of filament-induced breakdown signal production. Through wavefront optimization, we enhance the intensity of a chosen characteristic spectroscopic feature of copper by a factor of approximately 3 when performing filamentation over a 1-meter distance. The relative standard deviation of signal intensity is reduced from ∼17% to ∼12% after optimization. We find that modification of the wavefront by introduction of astigmatism and coma maximizes the signal intensity, and these aberrations appear in two distinct trials of the genetic algorithm. We compare these findings to previous work on multiple filament control and discuss the possible mechanisms that lead to signal enhancement associated with both the beam amplitude and phase profile. A broader use of wavefront control with feedback may improve the performance of FIBS in remote sensing applications.

Filament-induced breakdown spectroscopy with structured beams.

Filament-induced ablation represents an attractive scheme for long-range material identification via optical spectroscopy. However, the delivery of laser energy to the target can be severely hindered by the stochastic nature of multiple-filamentation, ionization of ambient gas, and atmospheric turbulence. In order to mitigate some of these adverse effects, we examine the utility of beam shaping for femtosecond filament-induced breakdown spectroscopy with Gaussian and structured (Laguerre-Gaussian, Airy, and Bessel-Gaussian) beams in the nonlinear regime. Interaction of filaments with copper, zinc, and brass targets was studied by recording axially-resolved broadband emission from the filament-induced plasma. The laser-solid coupling efficacy was assessed by inferring thermodynamic parameters such as excitation temperature and electron density. While under our experimental conditions the ablation rate with Gaussian- and Laguerre-Gaussian beams is found to be similar, the Airy and Bessel-Gaussian beams offer the advantage of longitudinally extended working zones. These results provide insights into potential benefits of structuring ultrafast laser beams for standoff sensing applications.

Plasma-grating-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a useful tool for determination of elements in solids, liquids, and gases. For nanosecond LIBS (ns-LIBS), the plasma shielding effect limits its reproducibility, repeatability, and signal-to-noise ratios. Although femtosecond laser filament induced breakdown spectroscopy (FIBS) has no plasma shielding effects, the power density clamping inside the filaments limits the measurement sensitivity. We propose and demonstrate plasma-grating-induced breakdown spectroscopy (GIBS). The technique relies on a plasma excitation source—a plasma grating generated by the interference of two noncollinear femtosecond filaments. We demonstrate that GIBS can overcome the limitations of standard techniques such as ns-LIBS and FIBS. Signal intensity enhancement with GIBS is observed to be greater than 3 times that of FIBS. The matrix effect is also significantly reduced with GIBS, by virtue of the high power and electron density of the plasma grating, demonstrating great potential for analyzing samples with complex matrix.

Effect of the distance between focusing lens and target surface on quantitative analysis of Mn element in aluminum alloys by using filament-induced breakdown spectroscopy* *Project supported by the National Natural Science Foundation of China (Grant No. 61575030), the Natural Science Foundation of Jilin Province, China (Grant Nos. 20180101283JC and 20200301042RQ), and the Fund from the Department of Education of Jilin

Ultrafast laser filament-induced breakdown spectroscopy (FIBS) is a potential technique for quantitative analysis of trace elements. In this work, we investigate the effect of the distance between focusing lens and target surface on the FIBS quantitative analysis of Mn element in aluminum alloys, and several major parameters are calculated such as the linear correlation coefficient (R 2), limits of detection (LOD), relative standard deviation (RSD), and root-mean-square error of cross-validations (RMSECV). The results show that the quantitative analysis parameter values before and after filament position are different. The optimal value can be obtained at the filament region, the average values of total 23 positions of R 2, LOD, RSD, and RMAECV were 99.45%, 1.41 mg/kg, 7.12%, and 0.56%, respectively. Besides, the spatial distributions of quantitative analysis parameter values in filament region are noticeable, and this is essentially due to intensity clamping effect in a filament.

Femtosecond Filaments for Standoff Detection of Explosives

In this report, we present our results from various studies to qualitatively discriminate the common military explosives viz. RDX, TNT and HMX in their pure form at a distance of ~6.5 m in standoff mode using femtosecond (fs) filament induced breakdown spectroscopy technique (fs FIBS) together with principal component analysis. A ~30 cm length fs filament obtained by a two-lens configuration was used to interrogate those energetic molecules in the form of pressed pellets (150 mg each). The plasma emissions were collected by a Schmidt-Cassegrain telescope (SCT) from a distance of ~8 m away from the investigation zone. Additionally, a few significant results obtained from the LIBS-based investigations of nitroimidazoles with respect to the standoff distance (~2 m) are discussed. Furthermore, we have also summarised a few important results from our recent investigations of bulk energetic materials in various configurations (including those with fs filaments). The results obtained from various fs FIBS configurations corroborate that the filament generation and its properties, the size and f-number of collection optics influence signal strength in the FIBS technique. These results project the fs FIBS technique as a potential technique for investigations aimed at hazardous materials and harsh environments in the standoff mode.

Standoff femtosecond filament-induced breakdown spectroscopy for classification of geological materials

Femtosecond (fs) filaments delivering substantial peak intensities at remote locations are exploited in classification of geological materials together within situ/standoff investigations.

Single-shot, multi-signature remote detection of uranium by filament-induced breakdown spectroscopy

Filament-induced breakdown spectroscopy (FIBS) is an attractive remote detection approach that is potentially applicable to nuclear materials such as uranium (U). Simultaneous detection of atomic U and U monoxide features is demonstrated in a single laser shot with detection probabilities of 52.2% and 39.0%, respectively, and with a 1% false-alarm probability. It is shown that a nearly 100% detection probability can be reached with 1% false-alarm probability in ≲1 second when using an 80 Hz laser and data acquisition system. Atomic U and uranium oxide (UO) signal features are identifiable in the remote measurement with comparable signal-to-background ratios, suggesting that, despite being broader than the U I emission line, the UO band is also suitable for remote detection of U by FIBS.

Remote discrimination of willow, pine and poplar trees and their growing environments by femtosecond filament-induced breakdown spectroscopy

Tree barks and leaves are increasingly used these days as environmental bioindicators for pollution assessment of their growing environment, but remote discrimination of tree species and their growing environments are rarely reported. Here the analytical potential of femtosecond filament induced breakdown spectroscopy (FIBS) for standoff detection and classification of different tree species and their growing environments is evaluated. A 800 nm, 40 fs Ti:Sapphire laser pulse is focused in air by a 2-m lens to generate a ~10–15 cm long single laser filament. The filament induces the emissions from willow, pine and poplar tree bark samples taken from two different environmental zones, i.e., a national park and a downtown business district (Changchun, China). The emission is detected in the backward direction with the bark samples located 2.5 m away from the detection system. Spectral signals, including molecular bands of CN, C2 and atomic lines of K, Ca, Mg, Na, Sr, Ba, Al, Fe and Mn are obtained from both smooth inner and rough outer surfaces of the bark samples, which can be used as spectral fingerprints. With the assistance of principal component analysis (PCA), simultaneous differentiation of the three tree species and their growing environments is presented, which shows a strong dependence on the tree species. Our results provide a promising strategy for remote, direct and fast tree species and environmental analysis.