An experimental and numerical study of laser-induced spark in air

Phuoc, Tran X.

doi:10.1016/j.optlaseng.2004.07.003

Cited by 85 publications

(20 citation statements)

References 22 publications

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“…The maximum spot radius was calculated to be 13.55 m and for a minimum input laser energy of 50 mJ, the minimum intensity was calculated to be Wcm . This was above the air breakdown threshold intensity of Wcm as given in [1], [4], and [14]. The detection system was an Ocean Optics LIBS2000+ Spectrometer.…”

Section: Experimental Setup and Proceduresmentioning

confidence: 90%

“…That is, the density had a concave parabollic shape as also observed in [21], within a plasma diameter of 0.5 mm around the axis. The slight hollow in the plasma could be due to a shock wave which blows the free electrons and compresses them against the cold neutral gas at the boundary [4]. This creates a slight void at the center of the plasma, while at the same time, cooling the plasma.…”

Section: A Electron Temperature and Densitymentioning

confidence: 99%

“…The first stage is breakdown as the gas is ionized, followed by laser energy absorption by the hot gas, and the last stage is detonation which results in plasma expansion and shock wave formation [2], [3]. The evolution of the plasma and the resulting shock waves have been studied both experimentally and theoretically [2], [4]- [6].…”

Section: Introductionmentioning

confidence: 99%

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Radial Variation of Refractive Index, Plasma Frequency and Phase Velocity in Laser Induced Air Plasma

Mathuthu

Raseleka

Forbes

et al. 2006

IEEE Trans. Plasma Sci.

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Abstract-Laser-induced breakdown spectroscopy (LIBS) is a nonintrusive technique that needs no sample preparation and even recently, quantitative measurements were done without the need for calibration standards. Much research has been done on the laser induced air plasma to study the spatial variation of plasma parameters in the axial direction of the laser beam. In this paper, we report investigation on the radial variation of the refractive index, plasma frequency, and phase velocity of a plasma during laser induced breakdown of air. The results show that the radial variations of the plasma frequency and refractive index are caused by the radial electron density gradient of the plasma. The radial variation of the electron density shows a noticeable depletion at the center of the focus which results in plasma phase velocities greater than the speed of light. Further from the plasma core the electron density diminishes to ambient density at the edges of the plasma. The mean full-width at half maximum (FWHM) for these plasma profiles was found to be about 1.2 mm. The results further reveal that the plasma has a concave parabollic electron density and a convex parabollic refractive index profile near the center of the laser axis, i.e., around a diameter of 0.5 mm.Index Terms-Laser-induced breakdown spectroscopy (LIBS), phase velocity, plasma frequency, refractive index.

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Section: Experimental Setup and Proceduresmentioning

confidence: 90%

Section: A Electron Temperature and Densitymentioning

confidence: 99%

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Radial Variation of Refractive Index, Plasma Frequency and Phase Velocity in Laser Induced Air Plasma

Mathuthu

Raseleka

Forbes

et al. 2006

IEEE Trans. Plasma Sci.

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“…The subsequent breakdown of air under the action of this spark was also studied (Zhuzhukalo et al, 1981). The same process was again studied (Phuoc, 2005) when this laser-induced spark had found ignition applications in internal combustion engines (Phuoc, 2006) due to the several advantages it offers over the conventional spark plug.…”

Section: Previous Studiesmentioning

confidence: 99%

Effect of Liquid Transparency on Laser-Induced Motion of Drops

Shukla

Sallam

2009

Journal of Fluids Engineering

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An experimental investigation of the role of liquid transparency in controlling laser-induced motion of liquid drops is carried out. The study was motivated by application to manipulation of liquid drops over a solid substrate. Droplets with diameters of 1–4 mm were propelled on a hydrophobic substrate using a pulsed-laser beam (532 nm, 10 Hz, 3–12 mJ/pulse) with a 0.9 mm diameter fired parallel to the substrate. The test liquid was distilled water whose transparency was varied by adding different concentrations of Rhodamine 6G dye. Motion of the drops was observed using a video camera. Measurements include direction of motion and the distance traveled before the drops come to rest. The present results show that the direction of the motion depends on the drop transparency; opaque drops moved away from the laser beam, whereas transparent drops moved at small angles toward the laser beam. The motion of both transparent and opaque drops was dominated by thermal Marangoni effect; the motion of opaque drops was due to direct heating by the laser beam, whereas in the case of transparent drops, the laser beam was focused near the rear face of the transparent drops to form a spark that pushed the drops in the opposite direction. Energies lower than 3 mJ were incapable of moving the drops, and energies higher than 12 mJ shattered the drops instead of moving them. A phenomenological model was developed for the drop motion to explain the physics behind the phenomenon.

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“…Even if the initial input energy was given, it will be needed to make hard effort to clarify the initial process of shock generation from the given condition due to the initial singularity at the energy source area such as initial energy discontinuity and strong non-equilibrium energy transfer in a very small region. Therefore, we will analyze the gas state behind the shock wave with a self-similar theory by Taylor and Sedov (12), (13) . Assuming the geometrical similarity for a plane, cylindrical and spherical blast wave, it can be analyzed in a self-similar coordinate with the similarity parameters, / across the shock front.…”

Section: Self-similar Analysismentioning

confidence: 99%

Optical Measurement of a Laser Induced Micro Shock Wave on a Metal Surface

Hirahara

Fujinami

Kawahashi

2008

JFST

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Laser induced streaming is one of the interesting phenomena. When we provide a highly concentrated energy in a small region with laser beam, an induced streaming, such as micro shock wave or laser induced thermal acoustics is observed in the region. In the present paper, a micro shock wave in air which was induced by laser irradiation was observed by the optical techniques. The shock wave was generated on the metal surface due to the laser ablation. In the present experiment, we focused on a relatively low irradiation intensity region. As the laser power decreased, the plasma plume was not observed clearly on the metal target, but a strong micro shock was still induced. The trajectory of shock front was recorded with the shadowgraphic measurement and the Mach number was calculated experimentally. Alternatively, the induced density behind the shock wave was measured by speckle photographic technique. The shock Mach number and density distribution was analyzed and discussed with self-similar theory.

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An experimental and numerical study of laser-induced spark in air

Cited by 85 publications

References 22 publications

Radial Variation of Refractive Index, Plasma Frequency and Phase Velocity in Laser Induced Air Plasma

Radial Variation of Refractive Index, Plasma Frequency and Phase Velocity in Laser Induced Air Plasma

Effect of Liquid Transparency on Laser-Induced Motion of Drops

Optical Measurement of a Laser Induced Micro Shock Wave on a Metal Surface

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