Glow-to-arc transition events in H2-Ar direct current pulsed plasma: automated measurement of current and voltage

The glow-to-arc transition phenomena (arcing) observed in plasma reactors used in materials processing was studied through the arcs characteristic current and voltage waveforms. In order to capture these arcs signals, a LABVIEW? based automated instrumentation system (ARCVIEW) was developed, including the integration of an oscilloscope equipped with proper current and voltage probes. The system also allows capturing the process parameters at the arc occurrence moments, which were used to map the arcs events conditions. Experiments in H(2)-Ar DC pulsed plasma returned signals data from 215 arcs events, which were analyzed through software routines. According to the results, an anti-arcing system should react in the time order of few microseconds to prevent most of the damage caused by the undesired arcing phenomena.     

Parallel free-space optical interconnect based on arrays of vertical-cavity lasers and detectors with monolithic microlenses

We investigate the use of low-threshold 980-nm vertical-cavity surface-emitting lasers for free-space optical interconnects. The vertical-cavity surface-emitting lasers and backilluminated detectors are monolithically integrated with microlenses on the back sides of the growth substrates to eliminate the necessity of external optics. With a channel pitch of 250 mum, an interconnect length between boards of the order of 5 to 10 mm with a ?50-mum lateral alignment tolerance can be achieved without external relay optics. The complete link is modeled to predict the system's efficiency and maximum bit rate. Data transmission at 500 Mbits/s per channel is demonstrated. The data rate was limited by parasitics, not the inherent bandwidth of the laser diodes.     

Porosity Depth Profiling of Thin Porous Silicon Layers by use of Variable-Angle Spectroscopic Ellipsometry: A Porosity Graded-Layer Model

Variable-angle spectroscopic ellipsometry was used to determine nondestructively the porosity depth profile and thickness of thin porous silicon layers produced by anodization of p(+)-doped silicon wafers. A porosity graded-layer model is presented and used in the analysis of the material. In the porosity graded-layer model an inhomogeneous layer is built up by several thin sublayers with the porosity changing slightly from one sublayer to the next. Results from the ellipsometry analysis and from transmission electron microscopy reveal inhomogeneous layers whose porosity and thereby optical properties change with their depth in the layers.     

Optical functions of transparent thin films of SrTiO(3), BaTiO(3), and SiO(x) determined by spectroscopic ellipsometry

A procedure is presented for accurately determining the thickness, optical functions, and surfaceroughness characteristics of thin-film insulators from two-channel spectroscopic polarization-modulation ellipsometry data. For films with minimal surface roughness, the optical functions can be determined over the entire measured spectrum; for rougher films, the analysis of the spectroscopic ellipsometry data yields meaningful values of the optical functions only in the transparent region. In general, the films must be transparent in a given range of wavelengths sampled by the ellipsometer so that at least two interference oscillations can be observed. The use of the procedure is illustrated with the determination of the optical functions of SrTiO(3) and BaTiO(3) thin films grown on MgO, and of SiO(x) films grown on Si. For SrTiO(3) and BaTiO(3), the thin-film results are compared with the measured optical functions of the respective bulk materials.     

Measurements of trapped protons and cosmic rays from recent Shuttle flights

Two new charged particle detectors have been flown in five recent Shuttle flights. The tissue-equivalent proportional counter measures the lineal energy spectrum of space radiation in the 0.26-300 keV micrometer-1 range. The charged particle spectrometer is a double dE/dx x E and dE/dx x Chrenekov detector system which provides a measurement of the differential energy spectrum of protons from 13 to 350 MeV and dose rate in silicon. In this paper the dose rate, equivalent dose rate, and radiation, quality factor for trapped protons and cosmic radiation are reported on separately. A comparison of the integral LET spectra with recent transport code calculations shows significant disagreement. Using the calculated dose rate from the omnidirectional AP8MAX model with IGRF reference magnetic field epoch 1970, and observed dose rate as a function of geographic latitude and longitude, the westward drift of the south Atlantic anomaly has been determined. The east-west effect has also been studied and a 'second' radiation belt observed. A comparison of the galactic cosmic radiation (GCR) lineal energy transfer spectra with model calculations shows disagreement comparable with those of the trapped protons.     

Polarization-induced noise in a fiber-optic Michelson interferometer with Faraday rotator mirror elements

Faraday rotator mirror elements have been used in a number of applications as compensators for induced birefringence in retracing paths. In interferometric systems, such as the fiber-optic Michelson interferometer, this approach proved to be useful in providing maximum fringe visibility and insensitivity to the polarization state of light injected into the interferometer. However, it is found that, when the characteristics of the fiber coupler depend on the polarization state of the input beam, the efficiency of the Faraday mirror elements is limited. Theoretical analysis and experimental results in support of this statement are presented.     

Ultrasound tomography system used for monitoring bubbly gas/liquid two-phase flow

This paper is about a transmission-mode (TM) ultrasound computerized tomography (UCT) system, which is used to monitor a bubbly gas/liquid two-phase flow, a kind of strongly inhomogeneous medium. Because of the high contrast in acoustic impedance distribution of the flow, TM UCT system can only obtain incomplete tomographic projections which depend on the distribution of bubbles in liquid. In order to describe this characteristic, a mathematical model was established. The algorithms used to reconstruct the profile of a distribution of bubbles over a 2-D cross-section of a pipe, for both parallel beam scanning geometry and fan-shape beam scanning geometry, were presented. By using a two-value (0/1) logical back-projection filtering algorithm, a real-time transmission-mode (TM) ultrasound computerized tomography (UCT) system involving fan-shape beam geometry had been developed. Both simulations and experiments showed that the performance of the system was acceptable with an image reconstruction speed of 41.7 frames per second and a data acquisition speed of 667 frames per second if a Pentium/90 compatible computer was used. Finally, possible future improvements of the system were discussed