Investigation of a gas breakdown process in a laser-plasma experiment

Soubacq, Stéphane; Pignolet, P.; Schall, Éric; Batina, John T.

doi:10.1088/0022-3727/37/19/012

Cited by 32 publications

(10 citation statements)

References 23 publications

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“…4, where we assume isothermal conditions in the core plasma, are used to calculate the plasma density decay rates over time when the plasma edge density and shock wave front are coincident and when the plasma size is large enough to obtain reliable density measurements, 600 nsՅ t Յ 2 s. The plasma density decay analysis is performed in this time window only in the core region of the plasma with a radius of r = Ϯ 1 mm, where negligible diffusion and isothermal ͑flat temperature͒ spatial profiles are assumed and indicated in other laser shock wave papers. 5,26 During this time window the measured electron density is n e Ն 10 15 cm −3 , in which the assumption of LTE is valid. 13,21 In the absence of an ionizing source, after the laser is turned off, the plasma decay can be described by the continuity equation 19,27 dn e dt = − D a ٌ 2 n e − v a n e − ␣ r n e 2 − ␤ e n e 3 , ͑11͒…”

Section: F Analysis Of Plasma Density Decaymentioning

confidence: 99%

Experimental investigation of ultraviolet laser induced plasma density and temperature evolution in air

Thiyagarajan

Scharer

2008

Journal of Applied Physics

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We present measurements and analysis of laser induced plasma neutral densities and temperatures in dry air by focusing 200 mJ, 10 MW high power, 193 nm ultraviolet ArF ͑argon fluoride͒ laser radiation to a 30 m radius spot size. We examine these properties that result from multiphoton and collisional cascade processes for pressures ranging from 40 Torr to 5 atm. A laser shadowgraphy diagnostic technique is used to obtain the plasma electron temperature just after the shock front and this is compared with optical emission spectroscopic measurements of nitrogen rotational and vibrational temperatures. Two-color laser interferometry is employed to measure time resolved spatial electron and neutral density decay in initial local thermodynamic equilibrium ͑LTE͒ and non-LTE conditions. The radiating species and thermodynamic characteristics of the plasma are analyzed by means of optical emission spectroscopy ͑OES͒ supported by SPECAIR, a special OES program for air constituent plasmas. Core plasma rotational and vibrational temperatures are obtained from the emission spectra from the N 2 C-B͑2+͒ transitions by matching the experimental spectrum results with the SPECAIR simulation results and the results are compared with the electron temperature just behind the shock wave. The plasma density decay measurements are compared with a simplified electron density decay model that illustrates the dominant three-and two-body recombination terms with good correlation.

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Section: F Analysis Of Plasma Density Decaymentioning

confidence: 99%

Experimental investigation of ultraviolet laser induced plasma density and temperature evolution in air

Thiyagarajan

Scharer

2008

Journal of Applied Physics

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“…Due to its fundamental nature, a large subset of this research has been devoted to studies of breakdown in air. [1][2][3][4] This paper reports experimental results of breakdown in air using sub-breakdown threshold intensity, 193 nm excimer laser radiation. Much of the theoretical basis of laser induced breakdown is based upon earlier work describing microwave breakdown.…”

Section: Introductionmentioning

confidence: 99%

Experimental measurements of multiphoton enhanced air breakdown by a subthreshold intensity excimer laser

Way

Hummelt

Scharer

2009

Journal of Applied Physics

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This work presents density, spectroscopic temperature, and shockwave measurements of laser induced breakdown plasma in atmospheric air by subthreshold intensity ͑5.5ϫ 10 9 W / cm 2 ͒ 193 nm laser radiation. Using molecular spectroscopy and two-wavelength interferometry, it is shown that substantial ionization ͑Ͼ10 16 cm −3 ͒ occurs that is not predicted by collisional cascade ͑CC͒ breakdown theory. While the focused laser irradiance is three orders of magnitude below the theoretical collisional breakdown threshold, the substantial photon energy at 193 nm ͑6.42 eV/ photon͒ compared with the ionization potential of air ͑15.6 eV͒ significantly increases the probability of multiphoton ionization effects. By spectroscopically monitoring the intensity of the N 2 + first negative system ͑B 2 ⌺ u + − X 2 ⌺ g + ͒ vibrational bandhead ͑vЈ =0,vЉ =0͒ at low pressure ͑20 Torr͒ where multiphoton effects are dominant, it is shown that two photon excitation, resonant enhanced multiphoton ionization is the primary mechanism for quantized ionization of N 2 to the N 2 + ͑B 2 ⌺ u + ͒ state. This multiphoton effect then serves to amplify the collisional breakdown process at higher pressures by electron seeding, thereby reducing the threshold intensity from that required via CC processes for breakdown and producing high density laser formed plasmas.

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“…This evolution feature is most likely related to the different generation and quenching mechanisms of their corresponding excited states. 42,43) A closer observation indicates that a similar or same temporal evolution profile is presented for each of the spectral lines with the relative humidity increased from 65, via 80, to 90 RH%. The temporal evolution for these characteristic spectral lines in different relative humidity further demonstrates that the influence of humidity on timeresolved emission spectra from air plasma is negligible.…”

Section: Time-resolved Emission Spectra Of Air Plasma For Various Rel...mentioning

confidence: 56%

“…It has been reported that in the laser-induced plasma, both the absorption coefficient due to inverse bremsstrahlung and the ionization rate in the case of photoionization grow with the laser irradiance at moderate levels. 42) The enhanced plasma absorption and growing photoionization promote the growth of ablation rate, which brings about the increase of electron density with respect to the laser irradiance, as shown in Fig. 7(d).…”

Section: Determination Of the Plasma Temperature And Electron Density...mentioning

confidence: 94%

Influence of humidity on the characteristics of laser-induced air plasma

Lei

Wang

et al. 2018

Jpn. J. Appl. Phys.

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The dependence of laser-induced breakdown spectroscopy (LIBS) on ambient conditions has not been clearly clarified as yet for element qualitative and quantitative analysis. To fill this gap, a laser-induced air plasma was produced by focusing a 1064-nm laser beam of Q-switched Nd:YAG pulse laser and the influence of relative humidity on the air plasma was systematically investigated by varying humidity at different laser irradiances. In contrast to the early findings, i.e., weak dependence of plasma properties on the humidity, some distinctive characteristics have been observed and explained. Examining the time-resolved emission spectra shows that the temporal evolution of spectral lines almost remains unchanged with the humidity and the influence of humidity on emission spectra can be neglected under a short gate width less than several hundred nanoseconds. As for the time-integrated emission spectra obtained at a higher laser irradiance, the increase in the emission intensity of H and O with the humidity is attributed to the increasing mole fraction of H and O and more laser energy that can be absorbed by the increasing water vapor. A faster growth of emission intensity of H and a slower increase of emission intensity of O respectively result from the relatively large increase of mole fraction of H and the relatively small increase of mole fraction of O with the humidity. Observations indicate that a shorter gate width or a lower laser irradiance is preferable in reducing the humidity influence and a certain magnitude of emission intensity of H and O spectral lines should be subtracted from the measured spectra for a more accurate and more reliable LIBS examination.

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Investigation of a gas breakdown process in a laser-plasma experiment

Cited by 32 publications

References 23 publications

Experimental investigation of ultraviolet laser induced plasma density and temperature evolution in air

Experimental investigation of ultraviolet laser induced plasma density and temperature evolution in air

Experimental measurements of multiphoton enhanced air breakdown by a subthreshold intensity excimer laser

Influence of humidity on the characteristics of laser-induced air plasma

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