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16 Oct 2000

Volume 77, Issue 16, pp. 2437-2616

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Initiation of an early-stage plasma during picosecond laser ablation of solids

Samuel S. Mao, Xianglei Mao, Ralph Greif, and Richard E. Russo

Appl. Phys. Lett. 77, 2464 (2000); http://dx.doi.org/10.1063/1.1318239 (3 pages) | Cited 40 times

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Picosecond time-resolved images of plasma initiation were recorded during pulsed-laser ablation of metal targets in an air atmosphere. An early-stage plasma was observed to form before the release of a material vapor plume. Close to the target surface, interferometry measurements indicate that the early-stage plasma has an electron number density on the order of 1020 cm−3. The longitudinal expansion of the ionization front for this plasma has a velocity 109 cm/s, during the laser pulse. In contrast, a material–vapor plume forms approximately 200 ps after the laser pulse, and it moves away from the target at 106 cm/s. The experimental observations of the early-stage plasma were simulated by using a theoretical model based on a two-fluids description of laser plasmas. The results indicate that the initiation of the plasma is due to air breakdown assisted by electron emission from the target. © 2000 American Institute of Physics.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
81.05.Bx Metals, semimetals, and alloys
79.20.Ds Laser-beam impact phenomena
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.-b Plasma properties
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys
81.65.-b Surface treatments

Diagnostics of inductively coupled chlorine plasmas: Measurements of the neutral gas temperature

V. M. Donnelly and M. V. Malyshev

Appl. Phys. Lett. 77, 2467 (2000); http://dx.doi.org/10.1063/1.1318727 (3 pages) | Cited 68 times

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We report measurements of the bulk, neutral gas temperature in a chlorine transformer-coupled plasma. A trace amount (2%–5%) of N2 was added to the discharge and the rotational temperature of the C3Πu state was determined from the C3Πu→B3Πg emission in the ultraviolet. This temperature has been shown by others to be equal to the rotational temperature of ground-state N2, which is the thermally equilibrated (translational and rotational) gas temperature (Tg). The gas temperature 3 cm above the wafer is equal to, or only slightly above the wall temperature (300 K) throughout the low-power, capacitively coupled regime (<60 W, 0.024 W/cm3). Between the lowest (130 W, 0.053 W/cm3) and highest (900 W, 0.36 W/cm3) inductively coupled mode powers investigated, Tg increases sublinearly with power (and electron density). The high-power (900 W) Tg increases with increasing pressure (650, 750, 900, and 1250 K at 2, 5, 10, and 20 mTorr, respectively). Mechanisms of neutral gas heating are discussed. The energy released in dissociation of Cl2 appears to be the dominant heating mechanism. © 2000 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
52.80.Pi High-frequency and RF discharges
33.20.Sn Rotational analysis
52.40.Hf Plasma-material interactions; boundary layer effects
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