Femtosecond Filament-induced Breakdown Spectroscopy Research Articles

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.

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.

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.

Standoff discrimination and trace detection of explosive molecules using femtosecond filament induced breakdown spectroscopy combined with silver nanoparticles

The potential of femtosecond filament induced breakdown spectroscopy technique (fs FIBS) towards the detection of explosive/energetic molecules (EMs) at a standoff (ST) distance of ∼6.5 m is demonstrated. A set of six energetic nitroimidazoles were investigated and discriminated with the fs FIBS technique in tandem with principal component analysis (PCA). The fs ST-FIBS spectra of these EMs were dominated with CN emissions with weak C2 emission and devoid of other atomic peaks (H, N, and O). In addition, an enhancement in LIBS/ST FIBS signal of EMs is achieved in the presence of Ag nanoparticles (NPs) using the nanoparticle enhanced LIBS (NELIBS) technique. Furthermore, the potential of fs filaments for detecting explosive traces is also demonstrated by detecting the residue of an explosive molecule CL-20 on a brass target using the fs NEFIBS technique.

Discrimination of bimetallic alloy targets using femtosecond filament-induced breakdown spectroscopy in standoff mode.

The femtosecond filament-induced breakdown spectroscopy (FIBS) technique coupled with principal component analysis (PCA) is demonstrated for standoff (ST) analysis of metals, alloys (Al, Cu, brass, stainless steel), and bimetallic strips (Ag@Cu, Ag@Au with varying weight percentages). The experiments were performed by analyzing the filament-produced plasma at ∼6.5 m from the laser. The plasma emissions were collected using a Schmidt-Cassegrain telescope (6″ f/10) at ∼8 m away. The variations in intensities of persistent atomic transitions in the FIBS spectra clearly reflected the varying weight percentage in bimetallic strips. Furthermore, PCA was successfully utilized to discriminate the metals, alloys, and bimetallic strips batch wise and altogether. Our results demonstrate the capability of femtosecond ST-FIBS for ST analytical applications.

Analysis of heavy metals in poplar leaves by femtosecond filament-induced breakdown spectroscopy

Femtosecond filament-induced breakdown spectroscopy (FIBS) is employed to qualitatively analyze the heavy metal elements (Ca, Fe and Cr) in poplar leaves, at the same age, from four representative locations in Changchun City, i.e. Changchun First Automobile Factory, Railway Station, Jingyue National Forest Park, and Changchun University of Science and Technology (CUST) in the same season. The stem and mesophyll from the same leaf are investigated as samples by the FIBS technique. Experimental results demonstrate that the concentration of Ca and Fe elements in the leaf stem are higher than those in the leaf mesophyll through comparing the spectral intensities of Ca Ⅱ 393.37 nm and Fe Ⅰ 422.87 nm. Based on the analysis of the FIBS spectral intensity of heavy metals mentioned above in the poplar leaves from the four different locations, the heavy metal elements Ca, Fe and Cr in the poplar leaves gathered from the Automobile factory area have the highest concentration among the four locations, and those from Jingyue National Forest Park are the lowest. The FIBS technique can obtain stable plasma spectrum for the poplar leaves with irregular surfaces because of the optical intensity clamping effect inside the femtosecond filament. This experiment demonstrates that FIBS can be utilized to find new applications in the environmental pollution on-site detection.

Detection of heavy metal Cr in soil by the femtosecond filament induced breakdown spectroscopy

In this paper, the element content detection of heavy metal Cr in soil is investigated experimentally by femtosecond filament induced breakdown spectroscopy (FIBS). The plasma filament length is measured using the fluorescence method, and the spatial distribution of Cr 425.5 nm spectral intensity is obtained at lens focal lengths 150 mm and 1000 mm. A calibration curve of the heavy metal element Cr in the soil is obtained based on experimental results. Results demonstrate that the relative deviation of the quantitative analytic result from the standard value is smaller than 5%, and the detection limit of Cr in soil is 7.85 ppm at the laser repetition rate 1 kHz. The femtosecond laser filaments induced breakdown spectroscopy is entirely feasible for quantitative detection of heavy metal element Cr in the soil.

Remote detection of similar biological materials using femtosecond filament-induced breakdown spectroscopy

We demonstrated the feasibility of remote detection and differentiation of some very similar agricultural-activity related bioaerosols, namely barley, corn, and wheat grain dusts, through nonlinear fluorescence of fragments induced by the high-intensity inside filaments of femtosecond laser pulses in air. The signals were detected in Lidar configuration with targets located at 4.7 m away from the detection system. All the species showed identical spectra, namely those from molecular C2 and CN bands, as well as atomic Si, C, Mg, Al, Na, Ca, Mn, Fe, Sr and K lines. These identical spectral bands and lines reveal similar chemical compositions; however, the relative intensities of the spectra are different showing different element abundances from these three bio-targets. The intensity ratios of different elemental lines were used to distinguish these three samples. Good reproducibility was obtained. We expect that this technique could be used at long distance and thus played as a sensor of similar biological hazards for public and defense security.