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26 Sep 2011

Volume 99, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 99, 131101 (2011); http://dx.doi.org/10.1063/1.3641907 (3 pages)

Linas Minkevičius, Vincas Tamošiūnas, Irmantas Kašalynas, Dalius Seliuta, Gintaras Valušis, Alvydas Lisauskas, Sebastian Boppel, Hartmut G. Roskos, and Klaus Köhler
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Fountain effect of laser-driven relativistic electrons inside a solid dielectric

G. S. Sarkisov, P. Leblanc, V. V. Ivanov, Y. Sentoku, V. Yu. Bychenkov, K. Yates, P. Wiewior, D. Jobe, and R. Spielman

Appl. Phys. Lett. 99, 131501 (2011); http://dx.doi.org/10.1063/1.3641862 (3 pages) | Cited 2 times

Online Publication Date: 26 September 2011

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Ultrafast interferometry with sub-ps resolution has been applied for the direct measurement of an electron density induced by a laser-driven relativistic electron beam inside a solid dielectric. The topology of the interference phase shift shows the signature of the “fountain effect,” a narrow electron beam that fans out from the propagation axis and heads back to the target surface. Two-dimensional particle-in-cell (PIC) computer simulations demonstrate radial spreading of fast electrons by self-consistent electrostatic fields. The very low ionization, ∼0.1%, observed after the heating pulse suggests a fast recombination at the sub-ps time scale.
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79.20.Ds Laser-beam impact phenomena
78.47.J- Ultrafast spectroscopy (<1 psec)
61.80.Fe Electron and positron radiation effects

An analysis on transmission microwave frequency spectrum of cut-off probe

D. W. Kim, S. J. You, B. K. Na, J. H. Kim, and H. Y. Chang

Appl. Phys. Lett. 99, 131502 (2011); http://dx.doi.org/10.1063/1.3634022 (3 pages) | Cited 5 times

Online Publication Date: 27 September 2011

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We investigated the formation mechanism of transmission microwave frequency (TMF) spectrum of cut-off probe using a simple circuit model to elucidate the physics behind the TMF spectrum. The result showed that the overall shape of the TMF spectrum of cut-off probe (N – shape spectrum) is well reproduced with our proposed circuit model and can be understood as the combined result of two different resonances caused by the elements between two probe tips (a sheath, a plasma, and a vacuum which is filled by the plasma). Furthermore, based on this simple modeling, a more precise method to find the plasma frequency by taking account with the e-n collision frequency and the pressure limitation of the cut-off probe application is established.
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52.70.Ds Electric and magnetic measurements
52.40.Kh Plasma sheaths
52.25.Tx Emission, absorption, and scattering of particles
52.20.Fs Electron collisions
52.70.Gw Radio-frequency and microwave measurements

Light emission phenomena in dechlorination process of polychlorinated biphenyls by irradiating microwave

A. Kumada, T. Morimoto, K. Hidaka, K. Amano, and K. Itoh

Appl. Phys. Lett. 99, 131503 (2011); http://dx.doi.org/10.1063/1.3644133 (3 pages)

Online Publication Date: 27 September 2011

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In recent years, an effective processing for PCBs (polychlorinated biphenyls) diluted in insulating oil has been developed, which can render PCBs harmless by their dechlorination using microwave of 2.45 GHz. The authors discovered optical emission of electrical discharge during the processing. To clarify how the emission is involved in the decomposition of PCBs, the emission spectra are two-dimensionally observed with interference filters. The observation reveals the generation of excited hydrogen atoms and ultraviolet photons, both of which accelerate the PCBs dechlorination, and suggests the presence of the electric-field effect of microwave other than its heat effect.
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78.55.Kz Solid organic materials
42.79.Ci Filters, zone plates, and polarizers
61.41.+e Polymers, elastomers, and plastics

Fast relaxation of the velocity distribution function of neutral and ionized species in high-power impulse magnetron sputtering

Nikolay Britun, Maria Palmucci, and Rony Snyders

Appl. Phys. Lett. 99, 131504 (2011); http://dx.doi.org/10.1063/1.3644989 (3 pages)

Online Publication Date: 28 September 2011

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A super-exponential time-relaxation of the full width at half maximum of Ti and Ti+ spectral lines was found during the off-time in a high-power impulse magnetron sputtering discharge studied by laser-induced fluorescence. After the estimation of the possible broadening mechanisms, the main contribution to the determined linewidths appeared to be the broadening due to ballistic motion of sputtered species with a minor contribution of the instrumental and Doppler broadenings. The deconvoluted linewidths depend both on pressure and distance from target, and their time-decay was attributed to the fast energy relaxation of the sputtered neutrals and ions during the off-time.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
32.70.Jz Line shapes, widths, and shifts
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
32.50.+d Fluorescence, phosphorescence (including quenching)
52.80.-s Electric discharges
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)

Performance characteristics according to the channel length and magnetic fields of cylindrical Hall thrusters

Jongsub Lee, Mihui Seo, Jongho Seon, Hae June Lee, and Wonho Choe

Appl. Phys. Lett. 99, 131505 (2011); http://dx.doi.org/10.1063/1.3643435 (3 pages) | Cited 1 time

Online Publication Date: 28 September 2011

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Performance characteristics of low power cylindrical Hall thrusters are investigated in terms of the length of the discharge channel. Thrust, efficiency, discharge current, and propellant utilization are evaluated for different channel lengths of 19, 22, and 25 mm. It is found that the propellant utilization and ion energy distribution function are strongly associated with the channel length. Increase of thrust and efficiency are also found with increasing channel lengths. These characteristics of the thruster are interpreted with possible generation of multi-charged ions due to increased residing time within the extended space inside the channel.
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52.75.Di Ion and plasma propulsion
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.80.-s Electric discharges
52.25.Fi Transport properties

Gas dynamic effects on formation of carbon dimers in laser-produced plasmas

K. F. Al-Shboul, S. S. Harilal, and A. Hassanein

Appl. Phys. Lett. 99, 131506 (2011); http://dx.doi.org/10.1063/1.3645631 (3 pages) | Cited 8 times

Online Publication Date: 29 September 2011

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We investigated the effect of helium and nitrogen pressures on the dynamics of molecular species formation during laser ablation of carbon. For producing plasmas, planar carbon targets were irradiated with 1064 nm, 6 ns pulses from an Nd:yttrium aluminum garnet laser. The emission from excited C2 and CN molecules was studied using space resolved optical time-of-flight emission spectroscopy and spectrally resolved fast imaging. The intensity oscillations in C2 and CN monochromatic fast imaging and their emission space-time contours suggest that recombination is the major mechanism of C2 formation within the laser ablation carbon plumes in the presence of ambient gas.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.38.Mf Laser ablation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
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