Plasma Excitation Temperature Research Articles

Optimizing Cu-alloy surface characteristics through magnetic field-enhanced fs laser treatment

We report here the effect of the magnetic field on plasma parameters and the surface structuring of the Cu alloy after fs laser irradiation. A Ti:Sapphire (800 nm, 35 fs, 1 KHz) laser is employed at various irradiances (0.011–0.117 PW/cm2) to generate plasma. A Transvers Magnetic Field (TMF) of strength 1.1 T is employed for plasma confinement. All the measurements were performed with and without TMF. The Cu plasma parameters, i.e., excitation temperature (Texc) and electron number sensity (ne), determined by laser-induced breakdown spectroscopy analysis, are higher in the presence of TMF. This magnetic field confinement of Cu plasma was studied analytically by evaluating thermal beta (βt), directional beta (βd), confinement radius (Rb), and diffusion time (td). To correlate Cu-alloy plasma parameters with surface modifications, field emission scanning electron microscope analysis is performed. It reveals the formation of low-spatial-frequency laser-induced periodic surface structures (LIPSSs) and high-spatial-frequency LIPSSs, along with agglomers and nano-rims formation. Distinct and well-defined structures are observed in the presence of a magnetic field. It is concluded that controlled surface structuring can be achieved through magnetic confinement, which enhances key plasma parameters. The technique has the potential for enhancing the fabrication of nano-gratings and field emitters, where spatial uniformity is critically important.

Examining the role of magnetic fields in plasma behavior and surface evolution of a Mg alloy with varied irradiances in a femtosecond laser treatment

This paper reports the effect of a magnetic field on plasma parameters and surface structuring of the Mg alloy after laser irradiation. Femtosecond pulses of a Ti:sapphire laser system (800 nm, 35 fs, 1 KHz) are employed as the source of irradiation at various irradiances ranging from 0.011PW/cm2 to 0.117PW/cm2 to generate ablated Mg-alloy plasma. A transvers magnetic field (TMF) of strength 1.1 Tesla is employed to confine laser generated Mg plasma. All the measurements are performed with and without TMF. The two plasma parameters, i.e., excitation temperature (Texc) and electron number density (n e ) of Mg plasma, have been evaluated by laser-induced breakdown spectroscopy (LIBS) analysis. It is observed that the values of Texc and n e of laser produced plasma (LPP) of the Mg alloy are higher in the presence of a magnetic field as compared to the field free case. Both show initially an increasing trend with increasing laser irradiance and after attaining their respective maxima a decreasing trend is observed with the further increase of irradiance. The magnetic confinement validity is confirmed by analytically evaluating thermal beta (β t ), directional beta (β d ), confinement radius (R b ), and diffusion time (t d ) for LPP of the Mg alloy. To correlate the LPP parameters of the Mg alloy with surface modifications a field emission scanning electron microscope (FE-SEM) analysis is performed. It was revealed that structures like laser-induced periodic surface structures (LIPSSs), agglomerates, islands, large sized bumps, along with channels and multiple ablative layers are observed. Distinct and well-defined surface structuring is observed in the presence of TMF as compared to the field free case. It is concluded that by applying an external magnetic field during laser irradiation, controlled material surface structuring is possible for fabrication of nanogratings and field emitters where spatial uniformity is critically important.

A rapid in-situ hardness detection method for steel rails based on LIBS and machine learning

The railway, as a public transportation system, has played a significant role in global economic development. However, the pursuit of high speed and heavy load in trains has brought significant bending and shear stresses on the rails, making the performance of steel rails a notable focal point. The properties of steel rails are crucial factors determining the operational safety of high-speed trains, while the surface hardness is regarded as a key mechanical characteristic. This study is to develop a new rapid in-situ method to measure the hardness of steel rails, by employing Laser-Induced Breakdown Spectroscopy (LIBS) and specified analysis technology. Three distinct methods, including spectral line intensity ratios, plasma excitation temperature and machine learning, have been compared and analysed. Particularly, a multivariate model is established and optimized using the machine learning methods for U71Mn steel rail hardness analysis. In the machine learning algorithms, variance normalization is utilized, resulted in a significant improvement for the information retention during the data dimensionality reduction process. Subsequently, twelve algorithm combinations were explored, revealing that the Particle Swarm Optimization employed in Support Vector Regression (PSO-SVR) yielded the lowest mean squared error (MSE). Further refinement of the PSO-SVR was achieved through the incorporation of adaptive stochastic weights, resulting in an elevated coefficient of determination (R2) to 0.9876. Finally, the performance of the model on the new five samples was validated with an R2 of 0.9864. Otherwise, its potential applicability may be extended to broader domains, providing robust support for enhancing the precision and reliability of LIBS technology in surface hardness quantitative analysis.

Comparison of excitation temperature of a laser-produced plasma by combining emission and absorption spectroscopy

Measurement of the temporal evolution of laser-produced plasma temperature is very important for many of its applications, and several plasma diagnostic tools are routinely used by researchers. However, it is very challenging to measure the properties of the plasma at the early and late times of its evolution using a single diagnostic tool. In this study, we combined emission and laser absorption spectroscopy to compare the excitation temperatures of a laser-produced uranium plasma system. Several U I transitions in the near-infrared spectral range (775–800 nm) were considered, and the Boltzmann plot method was used to measure the excitation temperatures using both emission and absorption spectroscopy. Emission spectroscopy provided early-time temperature measurements of the plasma up to times 2–20 µs, while absorption spectroscopy provided temperature measurements at late times of plasma evolution (for times 5–80 µs). The emission and absorbance of U I transitions were found to follow the Boltzmann distribution, indicating the plasma is likely in the state of local thermodynamic equilibrium even at late times of its lifetime. The emission and absorption-based time-resolved excitation temperatures demonstrated good agreement at earlier times (≤15 µs) in the overlapped temporal region, while a deviation in the measured values was seen at times (≥15 µs), and potential reasons for such a disagreement are discussed.

CF-LIBS based elemental analysis of Saussurea simpsoniana medicinal plant: a study on roots, seeds, and leaves.

The plant Saussurea Simpsoniana, which has been used in traditional medicine for its biocompatibility and abundant nutrients, offers a wide range of remedies. Local communities effectively utilize medicines derived from the plant's roots to treat various ailments such as bronchitis, rheumatic pain, and abdominal and nervous disorders. In this study, we present an elemental analysis of the chemical composition (wt%) of this medicinal plant using the laser-induced breakdown spectroscopy (LIBS) technique. In the air atmosphere, an Nd:YAG (Q-switched) laser operating at a wavelength of 532nm is utilized to create plasma on the sample's surface. This laser has a maximum pulse energy of approximately 400mJ and a pulse duration of 5ns. A set of six miniature spectrometers, covering the wavelength range of 220-970nm, was utilized to capture and record the optical emissions emitted by the plasma. The qualitative analysis of LIBS revealed the presence of 13 major and minor elements, including Al, Ba, C, Ca, Fe, H, K, Li, Mg, Na, Si, Sr, and Ti. Quantitative analysis was performed using calibration-free laser-induced breakdown spectroscopy (CF-LIBS), ensuring local thermodynamical equilibrium (LTE) and optically thin plasma condition by considering plasma excitation temperature and electron number density. In addition, a comparison was made between the results obtained from CF-LIBS and those acquired through energy-dispersive X-ray spectroscopy (EDX) analysis.

Effects of operational parameters on plasma characteristics and liquid treatment of a DBD-based unipolar microsecond-pulsed helium atmospheric pressure plasma jet

A dielectric-barrier-discharge-based square unipolar microsecond-pulsed helium atmospheric pressure plasma jet (APPJ) was characterized by combining a simplified equivalent circuit model with a transferred charge (Q) measured by introducing an additional capacitance in series with the reactor. From Q-V plots, Cd and Ccell for DBD reactors under pulsed excitation were determined. Q-V plots were drawn for varying operational parameters, and the dissipated energy per cycle was evaluated. Operational parameters, such as the gas flow rate and pulse frequency, were varied, and the resulting changes in the plasma plume length, gas temperature, excitation temperature, discharge current, dissipated power, and optical emission spectra were examined. As an example of the application of the plasma jet, liquid media, including de-ionized water, were exposed to the APPJ, and their properties (pH and electrical conductivity) and concentrations of reactive species generated in the media were measured as functions of the operational parameters. Furthermore, changes in the plasma-activated media after storage for different durations and under different conditions were examined. The correlation between plasma characteristics and properties of plasma-treated liquid is discussed.

Hydrogen from cellulose and low-density polyethylene via atmospheric pressure nonthermal plasma

The valorization of waste, by creating economic value while limiting environmental impact, can have an essential role in sustainable development. Particularly, polymeric waste such as biomass and plastics can be used for the production of green hydrogen as a carbon-free energy carrier through the use of nonthermal plasma powered by renewable, potentially surplus, electricity. In this study, a Streamer Dielectric-Barrier Discharge (SDBD) reactor is designed and built to extract hydrogen and carbon co-products from cellulose and low-density polyethylene (LDPE) as model feedstocks for biomass and plastic waste, respectively. Spectroscopic and electrical diagnostics, together with modeling, are used to estimate representative plasma properties, namely electron and excitation temperatures, number density, and power consumption. Cellulose and LDPE are plasma-treated for different treatment times to characterize the evolution of the hydrogen production process. Gas products are analyzed using gas chromatography to determine the mean hydrogen production rate, production efficiency, hydrogen yield, selectivity, and energy cost. The results show that the maximum hydrogen production efficiency for cellulose is 0.8 mol/kWh, which is approximately double that for LDPE. Furthermore, the energy cost of hydrogen production from cellulose is 600 kWh/kg of H2, half that of LDPE. Solid products are examined via scanning electron microscopy, revealing the distinct morphological structure of the two feedstocks treated, as well as by elemental composition analysis. The results demonstrate that SDBD plasma is effective at producing hydrogen from cellulose and LDPE at near atmospheric pressure and relatively low-temperature conditions in rapid-response and compact processes.

Effects of duty ratio on liquid- and polymer-surface treatment by a unipolar microsecond-pulsed helium atmospheric-pressure plasma jet

Effects of duty ratio of a unipolar microsecond-pulsed helium atmospheric-pressure plasma jet (APPJ) on liquid- and polymer-surface treatments were investigated. In addition, changes in the plasma plume length, gas temperature, excitation temperature, discharge current, absorption power, and optical emission spectra were examined by varying the other operating parameters, such as applied voltage and additive flow of oxygen or water vapor. As an example of liquid sample, de-ionized water (DW) was exposed to an APPJ, and the concentrations of the reactive species generated in the DW were measured as functions of the operating parameters. Polycarbonate, polypropylene, and polymethylmethacrylate were employed as exemplary substrate materials to investigate the effect of plasma treatment on polymeric surfaces. The APPJ treatment increased the surface energy and changed the wetting characteristics of the surface from hydrophobic to hydrophilic. X-ray photoelectron spectroscopy results showed that a short-time plasma treatment with He and/or He/O2, He/H2O affects the surface wettability owing to the introduction of polar groups.

Elemental study of Devarda’s alloy using calibration free-laser induced breakdown spectroscopy (CF‒LIBS)

In the present study, we present the compositional analysis of a Devarda’s alloy using the calibration–free laser-induced breakdown spectroscopy (CF-LIBS) technique. A nanosecond pulsed Q-switched Nd:YAG laser was focused on the target-sample under investigation to ablate its surface and the measured emission spectrum was registered by using a spectrometer (LIBS2000+) having the optical spectral within a range from 200–720 nm. The analysis of the measured optical spectra confirms the presence of three major elements Aluminum (Al), Copper (Cu), and Zinc (Zn) in the target sample. The emission intensity line profiles of Zn, Cu, and Al were utilized to estimate the plasma-parameters consisting of excitation temperature, and the plasma number density. The plasma excitation temperature was investigated using the Boltzmann-plot technique, which yields the temperature for Cu and Zn as 8547 ± 5% K and 8100 ± 5%, respectively, while the electron plasma density was calculated from the Stark-broadening of individual neutral emission lines of Al, Cu, and Zn. For the quantitative analysis of the elements that exist in the target sample, a CF-LIBS technique was employed by assuming the condition of optically thin plasma as well as local thermodynamics equilibrium. Using the CF-LIBS technique, the relative composition in the form of weight percentage was estimated to be Zn: 57%, Al: 39%, and Cu: 4%, whereas, the certified concentration of Devarda’s alloy was 50% for Zn, 45% for Al, and 5% for Cu. These measured results reveal that the elemental concentration utilizing CF-LIBS shows a reasonable agreement with standard estimates illustrated by the manufacturer. This study further suggests that the CF-LIBS technique opens up an opportunity for engineering and industrial usage of LIBS where a quantifiable study of the substance is exceedingly advantageous.

Effect of laser pulse duration on relative hardness estimation using LIBS

As the demand for a quick and remote way of hardness estimation increases, the attention to use LIBS for such application increases. Most of the studies of hardness estimation that have been done used nanosecond laser sources for LIBS while using femtosecond laser has not been studied yet. In this work, a group of five samples with different hardness were analyzed using nanosecond and femtosecond LIBS for relative hardness estimation. Almost the same wavelength was used to decrease the effect of wavelength as much as possible. Considering that the laser produced plasma is in a state of local thermodynamic equilibrium (LTE), the Boltzmann plot method was adopted to calculate the plasma excitation temperature (Te) which is closely correlated to the samples’ hardness. It was found that in case of nanosecond LIBS as the sample hardness increases the excitation temperature Te increases, while for the femtosecond LIBS the behavior was opposite and Te was found to be decreasing as the hardness of the target increases. This result may be attributed to the different plasma plume creation processes and its expansion for both nano- and femto- second lasers.

Spectroscopic Measurement of High Argon Jet Plasma Flow Rate for Methane Hydrate Decomposition

Methane hydrate is believed to contain a massive amount of potentially extractable hydrogen gas due to methane as the main component. A high-frequency argon jet plasma method has been proposed for decomposing hydrogen content. The excitation temperature of plasma can be directly observed from atomic emission lines. This information is more efficient to characterize the plasma behavior to optimize the decomposition process. In this study, the plasma excitation temperature was determined using spectroscopy and Boltzmann’s plot with a higher argon gas flow rate. An argon gas flow rate varied from 300, 400, 500, 1000, 1500, 2000, 2500, and 3000 mL/min. It flows inside a hollow tube in the counter electrode. A 27.12MHz high-frequency power source of plasma was applied to produce jet plasma at atmospheric pressure. The excitation temperature was observed in the range of 4310K to 5133K. The highest excitation temperature of 5133K was obtained at an argon gas flow rate of 500 mL/min.

A Spectrochemical Snapshot of Heavy Elements in Nile River Sediments: Line Intensity Calculation

ABSTRACT Nile River sediments were spectrochemically studied for the characterization of heavy elements. Ten sediment samples were milled and successfully pressed for obtaining homogeneously compact pellets. Their surface elemental analysis was obtained using ns-LIBS at two values of laser pulse energy: 25 mJ and 50 mJ. Despite the noticeable matrix effect, a snapshot visualizing the existing elements and their relative content detected in the investigated sediments is provided. The LIBS spectral data revealed the presence of some heavy elements such as Al, Ti, Fe, Mn, Ba, Co, Cr, Sr, and Cu in addition to other typical elements including Mg, Si, Ca, C, and Na. Their origin is easily linked to the illegal practices of the factories and companies discharging harmful wastes into the Nile, in addition to the probable agricultural sources. The LIBS results were supported and complemented by the XRD technique. Considering the inconsistent LIBS line intensity signal, a mathematical-based approach for spectral line intensity calculation is proposed. Assuring the existence of a local thermodynamic equilibrium condition (LTE), the plasma excitation temperature was determined for all samples using the Boltzmann plot (BP) applied to the spectral lines of MgI, FeI, CaI, and TiI, which cover different spectral regions. The BP linear fitting parameters and their averages are derived and exploited in calculating the spectral line intensity. The suggested method is claimed to theoretically adjust and balance any source of signal fluctuations arising from experimental conditions and/or instruments.

Influence of silicon particle morphology on laser-induced plasma properties

In this work, Si particles of varying sizes and a bulk Si wafer are exposed to high-energy nanosecond-pulsed laser excitation. The subsequent laser-induced plasma is characterized using a suite of diagnostic techniques, including spatiotemporal species imaging via high-speed videography and high-resolution gated spectroscopy. The intensity and location of various species in the plasma (e.g., Si I and Si II) are tracked as a function of time over two time regimes, 2–10 μs and 20–80 μs, and show differences in impurities and peak intensities between the various particle sizes and compared to the Si wafer. Electron densities under these conditions decrease from ≈1.8 to 0.8 × 1017 cm−3 from 2 to 8 μs, while plasma excitation temperatures determined from the Boltzmann method range from 9200 to 8000 K over the same time window. The powdered Si samples have characteristically larger and more intense plasmas than the wafer sample. The laser-induced air-shock from energetic materials (LASEM) method was employed on these materials, in concert with their acoustic response, to establish their relative microsecond energy releases. While the powders have similar laser-induced shock velocities, they appear to have differences in their acoustic response which roughly scales as a function of plasma carbon content. The proposed reasons for these shock and acoustic trends are discussed, which include particle size and morphology, surface impurities, and dispersion and flow within the plasma.

Emission enhancement in laser-induced breakdown spectroscopy from sample heating with a continuous-wave diode laser

In this work an affordable, energy-efficient technique to enhance the sensitivity of the laser-induced breakdown spectroscopy technique is presented. This method is based in applying the beam of a continuous wave (CW) diode laser into the spot where the focused beam of a pulsed Nd:YAG, high-power laser induces the plasma. With the present set-up the CW beam heats the sample's surface to 300 °C. It was found that pre-heating the target in this way increased the line intensity of both neutrals and ions by a factor of up to 4.5. It was also found that the plasma excitation temperature and the electron density of the heated sample did not differ significantly from those at room temperature. However the amount of ablated material did change significantly when the sample was heated, with the crater in the latter case as much as 8.9 times larger than that obtained at ambient temperature. We conclude that the intensification in the pre-heated-sample case stems not from increased electronic plasma density or temperature but rather from a larger plume size resulting from an increased amount of ablated material when the target is heated.

Electrical and Optical Test of a Semi-Combustible Plasma Generator via a Plasma Ignition Simulator

Electrothermal-chemical (ETC) launch technology can considerably increase the ballistic performance and optimize the fire range and range overlap of a 155-mm unimodular charge howitzer. To discuss the plasma ignition process of a semi-combustible plasma generator (SCPG) with a special tubular semi-combustible medium, a plasma ignition simulator (PIS) for the 155-mm unimodular charge howitzer is designed and manufactured to provide a realistic chamber environment. The optical and electrical measurements of a hybrid arc controlled ablation (ACA) plasma are operated via several sensors, a high-speed digital camera, and a compact spectrometer. Test results show that the PIS can satisfy the design requirements of the research of the plasma ignition process. When the discharge voltage is 6.5 kV, hybrid plasma propagation in the simulator chamber is observed and detected. The electronic excitation temperature of the hybrid plasma is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 15$ </tex-math></inline-formula> 860 K, and the hybrid plasma propagation velocity is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 1000$ </tex-math></inline-formula> m/s. These transient propagating hybrid plasmas are enough to ignite all unimodular charges in the chamber within 1.0 ms. The results provide an important reference for future ETC launch tests.

Probing plasma physics and elemental composition of a leonid meteor by fitting complex plasma radiation model parameters

ABSTRACT A numerical simulation model was developed and employed in elemental composition determination and characterization of meteor plasma physical parameters, particularly the plasma excitation temperature and electron density, by fitting the model parameters to the emission spectrum of a bright Leonid bolide recorded in the visible spectral range. Novel model introduced in this study involves self-absorption and enables parallel optimization of tens of the parameters. We also discuss that the observed bolide spectrum is strongly dependent on observation geometry.

Rapid Analysis of Chemical Composition and Physical Properties of Gemstones Using LIBS and Chemometric Technique

Laser-induced breakdown spectroscopy (LIBS), accompanied by chemometric data analysis, is used to identify and classify gemstones of various hardness. The study involves several gemstones: amethyst, aquamarine beryl, bloodstone citrine, diopside, and enstatite. Their hardness is determined through a correlation utilizing the spectral intensity ratio of the ionic to atomic spectral lines of an identified element in the LIB spectrum. The result of the relative hardness obtained from the LIBS analysis is in good agreement with the hardness measured from Mohs’s scale of hardness, a popular qualitative method to determine hardness. In this work, a linear relationship has been established between the Mohs’s hardness and the plasma excitation temperature. Thus, the hardness of the gemstones can be determined with the help of plasma excitation temperature. Moreover, the analysis of trace elements in LIB spectral data reveals that a particular element is responsible for the colors of gemstones. Therefore, the relative concentration of constituents is calculated for all gemstones and compared. Principal component analysis (PCA) is successfully applied to all gemstone spectra for rapid classification and discrimination based on their variable elemental concentrations and respective hardness.

Analysis of Lakhra Coal by Calibration Free Laser-Induced Breakdown Spectroscopy (CF-LIBS) and Comparison of Self-Absorption Correction Procedures

The analysis of Lakhra Coal to determine its total carbon content and ash content is reported by calibration-free laser-induced breakdown spectroscopy (CF-LIBS). The total carbon content and ash content in coal are key parameters for efficient energy u in sepower plants. The optical emission spectrum of coal contains spectral lines of Ca, Si, Fe, Ti, Mg, Na, K, Li, Al, and C together with traces of Ba and Sr. The excitation temperature and electron number density of the laser-produced plasma were estimated using a Boltzmann plot and Stark broadened Hα line, respectively. The self-absorption correction in the emission intensities of the spectral lines were performed using the internal reference self-absorption correction (IRSAC) and the density correction. The analysis of the coal was performed by CF-LIBS, CF-LIBS with IRSAC, and CF-LIBS with density correction which were then compared with the certified composition reported by the Lakhra Coal Development Company. The results revealed that IRSAC with a fixed slope is more easily applicable and reliable than the number density correction for analyzing the total carbon content, ash content, and trace elements.

Characteristics of plasma stream evolution in a pulsed plasma accelerator

The time-integrated spectroscopic measurements of argon plasma are carried out to characterize the transient plasma stream produced in a coaxial pulsed plasma accelerator. Transient plasmas produced in these types of devices have a temporal change in density and temperature. The temporal evolution of the plasma stream and its characteristic variation are studied from a time of 50–300 μs in steps of 50 μs. Analysis of different spectral lines shows the existence of some metastable states of Ar+ having a long lifetime. The evolution of different Ar+ transitions to metastable and non-metastable lower levels is observed for different time frames. From the Stark broadening and Boltzmann plot method assuming the partial local thermodynamic equilibrium model, the plasma densities and excitation temperatures are estimated. The temporal evolution study shows a decrease in plasma densities from 1.96 × 1021 m−3 at 50 μs to 1.23 × 1020 m−3 at 300 μs after the initiation of plasma formation. A reduction in excitation temperature is observed from 0.86 to 0.77 eV. Based on the density profile, the estimated energy density of the plasma stream shows a time-dependent decreasing trend from 0.06 to 0.004 MJ/m2 during the observed period. The results may be useful for optimization of the plasma stream in pulsed plasma accelerators concerning its different parameters.

Investigation of compositional analysis and physical properties for Ni-Cr-Nb alloys using laser-induced breakdown spectroscopy

In this work, laser-induced breakdown spectroscopy (LIBS) analysis is optimized for direct estimation of elemental composition, thermal conductivity and hardness for Ni-Cr-Nb alloys. These alloys were chosen with a variable elemental content of niobium and chromium. The influence of laser energy and shot numbers on measuring line intensity was investigated. Based on the ratio between two spectral lines, calibration curves were formed to estimate the element concentration and LIBS results were confirmed with related energy-dispersive X-ray spectroscopy (EDS) data. Hardness and thermal conductivity estimation using LIBS were done by measuring the ratio between two spectral lines, plasma excitation temperature and electron density for different samples. Semi-empirical formulas correlated hardness and thermal conductivity with plasma temperature were established.