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Title: Role of ambient gas and laser fluence in governing the dynamics of the plasma plumes produced by laser blow off of LiF-C thin film

Abstract

The time- and space-resolved emission profiles of Li I and Li II emission lines from the laser-blow-off plumes of a multilayered LiF-C thin film have been studied using spectroscopic technique. The evolution features were analyzed in different ambient environments ranging from high vacuum to 3 mbars of argon pressures and at various fluences of the ablating laser. During the evolution of the plume, a transition region was found to exist between 4 and 6 mm. Here, the plume dynamics changed from free expansion to collisional regime, where the plume experienced viscous force of the medium. The enhancement observed in neutral lines, in comparison with ionic lines, is explained in terms of the yield difference in electron impact excitation and ionization processes. Substantial difference in the arrival time distribution of the plume species was observed for Li I and Li II lines at high ambient pressures. Three expansion models are invoked to explain the evolution of the plume in different ambient conditions. The laser fluence was found to control the ratio of ions and neutrals.

Authors:
; ; ;  [1];  [2]
  1. Institute for Plasma Research, Bhat, Gandhinagar 382428 (India)
  2. (India)
Publication Date:
OSTI Identifier:
20982875
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 10; Other Information: DOI: 10.1063/1.2732446; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ABLATION; ARGON; CARBON; ELECTRON BEAMS; EVOLUTION; EXCITATION; ION EMISSION; IONIZATION; LASERS; LITHIUM FLUORIDES; PLASMA; PLASMA DIAGNOSTICS; PLUMES; THIN FILMS

Citation Formats

Singh, R. K., Kumar, Ajai, Patel, B. G., Subramanian, K. P., and Physical Research Laboratory, Navrangpura, Ahmedabad 380009. Role of ambient gas and laser fluence in governing the dynamics of the plasma plumes produced by laser blow off of LiF-C thin film. United States: N. p., 2007. Web. doi:10.1063/1.2732446.
Singh, R. K., Kumar, Ajai, Patel, B. G., Subramanian, K. P., & Physical Research Laboratory, Navrangpura, Ahmedabad 380009. Role of ambient gas and laser fluence in governing the dynamics of the plasma plumes produced by laser blow off of LiF-C thin film. United States. doi:10.1063/1.2732446.
Singh, R. K., Kumar, Ajai, Patel, B. G., Subramanian, K. P., and Physical Research Laboratory, Navrangpura, Ahmedabad 380009. Tue . "Role of ambient gas and laser fluence in governing the dynamics of the plasma plumes produced by laser blow off of LiF-C thin film". United States. doi:10.1063/1.2732446.
@article{osti_20982875,
title = {Role of ambient gas and laser fluence in governing the dynamics of the plasma plumes produced by laser blow off of LiF-C thin film},
author = {Singh, R. K. and Kumar, Ajai and Patel, B. G. and Subramanian, K. P. and Physical Research Laboratory, Navrangpura, Ahmedabad 380009},
abstractNote = {The time- and space-resolved emission profiles of Li I and Li II emission lines from the laser-blow-off plumes of a multilayered LiF-C thin film have been studied using spectroscopic technique. The evolution features were analyzed in different ambient environments ranging from high vacuum to 3 mbars of argon pressures and at various fluences of the ablating laser. During the evolution of the plume, a transition region was found to exist between 4 and 6 mm. Here, the plume dynamics changed from free expansion to collisional regime, where the plume experienced viscous force of the medium. The enhancement observed in neutral lines, in comparison with ionic lines, is explained in terms of the yield difference in electron impact excitation and ionization processes. Substantial difference in the arrival time distribution of the plume species was observed for Li I and Li II lines at high ambient pressures. Three expansion models are invoked to explain the evolution of the plume in different ambient conditions. The laser fluence was found to control the ratio of ions and neutrals.},
doi = {10.1063/1.2732446},
journal = {Journal of Applied Physics},
number = 10,
volume = 101,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • We report a systematic investigation of two plume interactions at different spatial separation (3-7 mm) in laser-blow-off. The plasmas plumes are created using Laser-blow-off (LBO) scheme of a thin film. The fast imaging technique is used to record the evolution of seed plasmas and the interaction zone which is formed as a result of interaction of the two seed plasmas. Time resolved optical emission spectroscopy is used to study evolution of optical emissions of the species present in the different regions of the plasmas. Neutral Li emissions (Li I 670.8 nm (2s {sup 2}S{sub 1/2} ← 2p {sup 2}P{sub 3/2,1/2}) and Limore » I 610.3 nm (2p {sup 2}P{sub 3/2,1/2} ← 3d {sup 2}D{sub 3/2,5/2})) are dominant in the plasmas but significant differences are observed in the emission and estimated plasma parameters of the seed and the interaction zone. The transport of plasma species from the seed plasmas to the interaction zone is discussed in the terms of plume divergence, kinetic energy of particles, and ion acoustic speed. An attempt is made to understand the formation and dynamics of the interaction zone in the colliding LBO seed plasmas.« less
  • The effects of mass and pressure of ambient gas on the propagation dynamics of two laser-blow-off plasma plumes created in close proximity are investigated. A time gated fast imaging technique is used for recording the images of the laterally colliding plumes under different experimental conditions. Pressure is varied from 0.1 to 3 mbar in three ambient, i.e., helium, neon, and argon. Emphasis is given on the nature of shock-shock interaction under different ambient conditions. It has been observed that the shock-velocity, shape, strength, and their interactions are strongly dependent on the mass and density of the ambient gases. The rolemore » of the interacting shocks and their subsequent reflections on the formation and geometrical shape of the interaction region in different ambient conditions is briefly described.« less
  • The temporal profiles of the spectral lines Li I and Li II emitted by a laser blow off of LiF-C film were analyzed. Fast neutrals having energies of {approx}310 eV were observed. It was found that these fast neutrals have kinetic energies similar to that of the ablated ions. Photon production rates at 670.8 nm were estimated for the recombination and charge exchange processes. We attempted to qualitatively understand the role of electron-ion recombination (two and three body recombinations) and charge exchange processes in producing observed fast neutrals. Our analysis indicates that charge exchange is the dominant process in themore » production of fast neutrals.« less
  • Two dimensional numerical modelling based on simplified hydrodynamic evolution for an expanding plasma plume (created by laser blow off) against an ambient background gas has been carried out. A comparison with experimental observations shows that these simulations capture most features of the plasma plume expansion. The plume location and other gross features are reproduced as per the experimental observation in quantitative detail. The plume shape evolution and its dependence on the ambient background gas are in good qualitative agreement with the experiment. This suggests that a simplified hydrodynamic expansion model is adequate for the description of plasma plume expansion.
  • The triple probe technique has been used to study the parameters of flowing plasma plume formed by laser-blow-off (LBO) of a multicomponent LiF-C target. The advantages of triple Langmuir probe over the single probe have been discussed with regard to the present study. Our results show that triple probe is better suited for parametric measurements close to the target. The spatiotemporal evolutions of electron density and temperature were measured in different ambient environments and for various laser fluences. The angular distribution of electron density and temperature was also measured. It was found that the presence of ambient gas drastically affectsmore » the electron density and temperature of the LBO plume. Large enhancement in n{sub e} and T{sub e} at intermediate pressures (10{sup -2} Torr) is expected due to increase in collisional processes. On the other hand, laser fluence does not affect the observed n{sub e} and T{sub e} significantly. In vacuum, a new phenomenon, i.e., an oscillation in the trailing portion of the plasma plume at a closer distance from the target, is also reported.« less