Large scale wavelike patterns are observed on an aluminum surface after it is ablated by a series of KrF laser pulses ͑248 nm, 40 ns, 5 J/cm 2 ͒. These surface structures have a wavelength on the order of 30 m, much longer than the laser wavelength. We postulate that these wave patterns are caused by the Kelvin-Helmholtz instability at the interface between the molten aluminum and the plasma plume. A parametric study is given in terms of the molten layer's thickness and of the spatial extent and kinetic energy density in the laser-produced plasma plume. Also included is an estimate of the cumulative growth in a multipulse laser ablation experiment. These estimates indicate that the Kelvin-Helmholtz instability is a viable mechanism for the formation of the large scale structures.

The channelspark, a low accelerating voltage, high current electron beam accelerator, has been used for ablation of materials applied to thin film deposition. The channelspark operates at accelerating voltages of 10 to 20 kV with ϳ1500 A beam currents. The electron beam ionizes a low-pressure gas fill ͑10-20 mTorr Ar or N 2 ) to compensate its own space charge, allowing ion focused transport. Ablation of TiN, Si, and fused silica has been studied through several plasma diagnostics. In addition, thin films of SiO 2 have been deposited and analyzed. Strong optical emission from ionized species, persisting for several microseconds, was observed in the electron beam ablated plumes. Free electron temperatures were inferred from relative emission intensities to be between 1.1 and 1.2 eV. Dye-laser-resonance-absorption photography showed Si atom plume expansion velocities from 0.38 to 1.4 cm/s for several pressures of Ar or N 2 background gas. A complex, multilobed plume structure was also observed, yielding strong indications that an electron beam instability is occurring, which is dependent upon the conductivity of the target. Nonresonant interferometry yielded line-averaged electron densities from 1.6 to 3.7ϫ10 23 m Ϫ3 near the target surface. Resonant UV interferometry performed on Si neutral atoms generated in the ablation plumes of fused silica targets measured line integrated densities of up to 1.6ϫ10 16 cm Ϫ2 , with the total number of ablated silicon neutrals calculated to be in the range 2.0ϫ10 15 to 5.0ϫ10 13 . Electron beam deposited films of fused silica were microscopically rough, with a thickness variation of 7%. The average SiO 2 deposition rate was found to be about 0.66 nm/shot. The electron beam-deposited fused silica films had accurately maintained stoichiometry. Ablated particulate had an average diameter near 60 nm, with a most probable diameter between 40 and 60 nm. For SiO 2 targets, the mass of material ablated in the form of particulate made up only a few percent of the deposited film mass, the remainder being composed of atomized and ionized material.

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This paper presents a technology in microthruster design: the ferroelectric plasma thruster (FEPT). The FEPT utilizes an applied rf electric field to create plasma on the surface of a ferroelectric dielectric. Acceleration of ions from this plasma provides thrust. Advantages of the FEPT include emission of both electrons and ions leading to self-neutralization, creation of plasma, and acceleration of ions with a single power supply, and application of thrust in a short amount of time. We present the concept of the thruster, operational physics, as well as experimental results demonstrating plasma creation and ion acceleration. These results along with plasma spectroscopy allow us to calculate thruster parameters.