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Jinto Thomas

Publications and source records attributed to Jinto Thomas.

12 recordsLinked to original sources
arXiv2026

A Comprehensive Study on the Line Profiles and Stark Widths of Ionic Transitions from Laser Produced Aluminum Plasma

We present a systematic spectroscopic investigation of laser-produced aluminum plasma to address inconsistencies in Stark broadening parameters and establish a self-consistent reference datasets for electron density diagnostics. Optical line emissions of Al II and Al III in the visible wavelength range were recorded from plasmas having different electron densities and temperatures, however, with the same experimental configuration, only by varying the background pressure, spatial positions, and delay time. The Stark width parameter of Al III lines, which shows consistency across different earlier studies, is used for standardizing the Al II transition from the highest energy level, which is abundant in the emission spectra. This reference spectrum is then used to estimate the Stark parameters of other Al II transitions to obtain a self-consistent database for Al II transitions. This approach significantly reduces the uncertainty in the estimated plasma electron density using Stark parameters of multiple emission lines. We also report the spatial and temporal evolution of plasma density and Stark shift as well as asymmetry in spectral lines. This work addresses the uncertainty in Stark parameters of Al II transitions in the visible range through a unified approach in estimating these parameters simultaneously.

physics.plasm-ph↗
arXiv2025

On the enhanced Balmer emission of hydrogen in helium Capacitively Coupled Radio Frequency (CCRF) plasma

The present study investigates the observation and enhancement in the intensity of the hydrogen Balmer series emission in a He CCRF plasma using optical emission spectroscopy (OES). In addition to the characteristic line emission of He atoms, the Balmer series of hydrogen and the molecular emission of N2 are also observed in the He discharge. These emissions were primarily attributed to the presence of water vapor in the chamber. In order to confirm the role of He, the study is also performed using air and Ar where no such Balmer series emissions is seen. Experimental evidence suggests that He metastables transfer energy to trace amount of water content present in the vacuum chamber. The results point towards the hypothesis that energy exchange between metastable He and water molecules could be the underlying mechanism. Since the energy of He metastables exceeds the ionization energy of H or H2O molecule, Penning ionization is expected to occur upon their interaction. The H ions formed as a result, consequently recombine with electrons in the plasma, emitting the Balmer series. Furthermore, the emission intensity of the Balmer series of H depends on the electron density of the He plasma. Experiments also show significant deviations in the intensity ratios of the Balmer series from conventional discharges, indicating difference in the underlying population mechanism. A Collisional Radiative (CR) model for measured plasma parameters was used to estimate the metastable population density to understand the mechanism behind the enhancement of the emission intensity. The increase in the metastable densities as well as the radiative recombination cross section appear to be responsible for the observed enhancement. We believe these results will be significant in terms of applications, in addition to providing a fundamental understanding of energy transfer between metastables of He and H2O.

physics.plasm-ph↗
arXiv2024

Effect of ambient on the dynamics of re-deposition in the rear laser ablation of a thin film

In this work, we report an innovative pump-probe based experimental set up, to study the melting, subsequent evaporation, plasma formation and redeposition in a thin film coated on a glass substrate under different ambient conditions and laser fluences. The ambient conditions restrict the expansion of the plasma plume. At high ambient pressure, plume expansion stops closer to the substrate and get re-deposited at the site of the ablation. This helps in the identification of multiple processes and their temporal evolutions during the melting, expansion and re-deposition stages. The ambient conditions affect the plasma plume formed upon ablation, thus modulating the transmission of probe laser pulses, which provides information about the plume dynamics. Further, the study offers valuable insights into the laser-based ablation of thin film coatings, which will have implications in in situ cleaning of view ports on large experimental facilities such as tokamaks and other systems e.g. coating units, pulsed laser deposition, Laser induced forward transfer, Laser surface structuring, etc.

physics.plasm-ph↗
arXiv2024

Effect of polarization on spectroscopic characterization of laser produced aluminium plasma

Laser-induced breakdown spectroscopy (LIBS) is a well-established technique widely used in fundamental research and diverse practical fields. Polarization-resolved LIBS, a variant of this technique, aims to improve the sensitivity, which is a critical aspect in numerous scientific domains. In our recent work we demonstrated that the degree of polarization (DOP) in the emission depends on the spatial location and time in a nano second laser generated aluminium plasma1. Present study investigates the effect of polarized emission on the estimation of plasma parameters. The plasma parameters are estimated using the conventional spectroscopic methods such as Boltzmann plot and line intensity ratio for the estimation of electron temperature and Stark broadening for estimating the electron density. The estimated plasma temperature using Boltzmann plot method shows large errors in electron temperature for the locations where DOP is higher. However, the electron density estimated using the Stark width does not show such variation. The observed ambiguity in temperature estimation using the Boltzmann plot method appears to be a consequence of deviation from expected Maxwell Boltzmann distribution of population of the involved energy levels. These findings highlight the need of assessing the DOP of the plasma before selecting the polarization for PRLIBS or temperature estimation using Boltzmann plots in elemental analysis.

physics.plasm-ph↗
arXiv2023

Spatio-temporal dynamics of anisotropic emission from nano second laser produced aluminium plasma

Polarized emission carries captivating information and can help understand various elementary processes involving collisions within the plasma as well as in radiative transitions. In this work, we investigate the spatio-temporal dependence of the emission anisotropy of a nanosecond laser produced aluminium plasma at 100 mbar background pressure. We observe that the anisotropy of the emission spectra exhibits interesting spatio-temporal characteristics which in turn depend on the charge state of the emitting species. The degree of polarization (DOP) is found to reverse its sign along the plume propagation direction. Observed behaviour in DOP appears to be due to the contribution from various involved atomic processes. However, closer to the sample the contribution from the self-generated magnetic field predominantly affect the polarization. On the other hand, the effect of the self generated magnetic field on the observed polarized emission is insignificant as the plume propagates away from the sample. This is of particular interest in polarization resolved laser induced breakdown spectroscopy as spatio-temporal profile of the degree of polarization has to be properly taken into account prior to the spectral analysis.

physics.plasm-ph↗
arXiv2023

Shielded ionisation discharge (SID) probe for spatio-temporal profiling of pulsed molecular beam

In this work we report a shielded ionization discharge (SID) probe which is conceptualized, designed and implemented for measuring temporal and spatial density profiles in a pulsed molecular beam. The probe detects and provides profiles of neutrals of the molecular beam using small discharge which is assisted by the thermionic emission of electrons from a hot filament. In this article, design and characterisation of the developed probe are discussed. The performance of the probe is demonstrated by measuring the spatio-temporal profile of a 1.5 ms pulsed supersonic molecular beam. The suggested SID probe can be used to characterize and optimise the pulsed molecular beam source used in tokamak fueling, SMBI plasma diagnostics, ion beam profile monitors, cluster beam experiments, chemical kinetics, and other supersoinc beam related applications.

physics.plasm-ph↗
arXiv2022

Experimental investigation of free jets through supersonic nozzles

In this paper, we report experimental investigation to improve the shape of a supersonic nozzle for rarefied flows to generate high axial density at extended distances from the nozzle. The reported work is significant for molecular jet/beam applications that require high center-line density and narrow jet profile. We investigate a parabolic nozzle whose profile is generated using the virtual source model of free expansion and compare its performance with a set of conical nozzles having different cone angles using simulations as well as experiments. All nozzles are made by additive manufacturing using ABS and performance is found to be satisfactory. Axial density and lateral spread of the jets are measured using a pitot tube assembly. The accuracy and operational limit of the pitot tube for rarefied flow is quantified by using established mathematical and empirical models for a sonic nozzle. The study demonstrates that the performance of the parabolic nozzle is comparable or slightly better as compared to conical counterparts. Moreover, the parabolic profile can be used for optimizing the opening angle for conical nozzles of various lengths.

physics.flu-dyn↗
arXiv2022

On the delayed emission from laser produced aluminum plasma under argon environment

In this article, we report rather long time emission ($\sim$ 250 $μs$) from aluminum neutrals (Al I) in ns laser produced plasma in the presence of ambient argon. The study is carried out with varying laser power density, background pressure, and the distance from the target. Slow and fast peak components in the emission spectra observed at earlier times are well reported. However, interestingly a very long delayed emission is also observed for the first time which depends on laser power density, distance from the target, ambient gas and pressure. The emission is observed from Al neutrals only. The most likely mechanism of this emission appears to be the excitation and subsequent emission from Al neutrals as a result of energy transfer from metastables of the ambient gas.

physics.plasm-ph↗
arXiv2022

Anomalous time of flight behavior of fast ions in laser produced aluminum plasma

In this work, dynamics of multi-charged ions emitted from an aluminum plasma produced by Q switched Nd: Yag laser is studied using time of flight (TOF) measurements from Langmuir Probe (LP) and spectroscopy (STOF) under Ar ambient of 0.02 mbar. The temporal evolution of multi-charged ions, background neutrals and ions is systematically studied for varying laser intensities. The temporal evolution shows all the species have double peak structure for all the laser intensities considered in the study. The fast peak is sharp whereas the slow peak is broad similar to that observed in previous studies. Moreover, higher charged ions have higher velocity, indicating acceleration from the transient electric field produced at the very initial temporal stages of expansion. Interestingly, the fast peak gets delayed, whereas the slow peak advances in time with increased laser intensity, which has not been reported in earlier studies. The observations point towards the possible role of ambipolar electric fields in the unexpected observed behavior of the TOF profiles.

physics.plasm-ph↗
arXiv2021

Flow characterization of supersonic gas jets: Experiments and Simulations

In present work, we report an experimental setup that has been developed to characterize highly under-expanded helium and nitrogen jets confined in a vacuum chamber. The evolution of Zone of Silence (ZOS) is studied and found that experimentally measured ZOS for helium and nitrogen jets are in agreement with empirical relation and mathematical model. The velocity of the jet inside ZOS is measured using a developed time of flight (TOF) probe without using a skimmer. We are able to measures the velocity of the gas jet itself compared to a skimmer-based method which measures the velocity of gas that is subjected to further expansion after the skimmer. Moreover, this method is free from skimmer interference and calibration involved with it. We observe that the measured velocity for helium is smaller than the terminal velocity. This can be attributed to losses which can occur due to nozzle geometry. Simulations are carried out using available DS2V code. Experimentally observed velocities of jets inside ZOS are compared with simulated values and are found to be in agreement within experimental uncertainties.

physics.flu-dyn↗
arXiv2020

Observation of ion acceleration in nanosecond laser generated plasma on a nickel thin film under forward ablation geometry

In this article we report acceleration observed for ions in a forward ablation geometry of 50 nm thick nickel film coated on a glass plate under nanosecond laser ablation. A detailed study with varying background pressure and laser energy of time of flight (TOF) spectra of ionic and other neutral transitions from plasma is undertaken. The results indicate that TOF spectra recorded for different neutral transitions exhibit different dynamical behavior (the slower peak of the neutral emission becomes faster with background pressure). Similar observation is seen for the ionic species as well. These observations have similarity to some of the reported double-layer concepts. However, the calculated electric fields from the acceleration appear to be anomalously higher. Along with the acceleration observed for the ionic and neutral lines, significant asymmetry in spectral shape is observed for neutral nickel line (712.2 nm) along with spectral broadening as the background pressure increases. This large asymmetry is indicative of micro electric fields present inside the laser produced plasma plume which may result in a continuous acceleration of ions. Interestingly, the asymmetry in spectral broadening exhibits temporal and spatial dependence which indicates that electric field is present in the plasma plume even for longer duration and also over a significant distance.

physics.plasm-ph↗