Polarization properties and fractional-power analysis of coated and uncoated parallel-slab multireflection beam splitters

The polarization properties of coated and uncoated parallel-slab multireflection beam splitters are investigated. In a recent study [Opt. Lett. 21, 1709 (1996)] it was shown that the parallel-slab beam splitter is a basic optical component of the parallel-slab division-of-amplitude photopolarimeter. The ellipsometric parameters and the fractional powers for multireflected components generated by this system are analyzed. Interesting new observations with respect to the polarization properties at the Brewster angle of incidence and the distribution of powers among the multireflected components are presented.     

Improved fingerprint identification with supervised filtering enhancement

An important step in the fingerprint identification system is the reliable extraction of distinct features from fingerprint images. Identification performance is directly related to the enhancement of fingerprint images during or after the enrollment phase. Among the various enhancement algorithms, artificial-intelligence-based feature-extraction techniques are attractive owing to their adaptive learning properties. We present a new supervised filtering technique that is based on a dynamic neural-network approach to develop a robust fingerprint enhancement algorithm. For pattern matching, a joint transform correlation (JTC) algorithm has been incorporated that offers high processing speed for real-time applications. Because the fringe-adjusted JTC algorithm has been found to yield a significantly better correlation output compared with alternate JTCs, we used this algorithm for the identification process. Test results are presented to verify the effectiveness of the proposed algorithm.     

A fast CAD model of plasma spread in thyristors using aseminumerical time-domain approach

This paper presents a fast CAD model to calculate plasma-spreading velocity in large area thyristors. The model is based on the two-dimensional two-transistor circuit model of a thyristor. At first, a simplified numerical solution of the semiconductor equations is developed to obtain the current amplification factor and the base transit time of each transistor of the thyristor model as a function of the emitter current density. The turn-on recurrence relations governing the evolution of the anode current at different lateral points are then derived by the transit function method. The time constant of the anode current rise and the plasma spreading velocity are calculated as functions of the anode current density. The results of simulation are in close agreement with the corresponding measured values of plasma spreading velocity by the electrical probes method. This agreement confirms the validity of our model over a large scale of anode current densities     

Performance optimization and light-beam-deviation analysis of the parallel-slab division-of-amplitude photopolarimeter

A division-of-amplitude photopolarimeter that uses a parallel-slab multiple-reflection beam splitter was described recently [Opt. Lett. 21, 1709 (1996)]. We provide a general analysis and an optimization of a specific design that uses a fused-silica slab that is uniformly coated with a transparent thin film of ZnS on the front surface and with an opaque Ag or Au reflecting layer on the back. Multiple internal reflections within the slab give rise to a set of parallel, equispaced, reflected beams numbered 0, 1, 2, and 3 that are intercepted by photodetectors D(0), D(1), D(2), and D(3), respectively, to produce output electrical signals i(0), i(1), i(2), and i(3), respectively. The instrument matrix A, which relates the output-signal vector I to the input Stokes vector S by I = AS, and its determinant D are analyzed. The instrument matrix A is nonsingular; hence all four Stokes parameters can be measured simultaneously over a broad spectral range (UV-VIS-IR). The optimum film thickness, the optimum angle of incidence, and the effect of light-beam deviation on the measured input Stokes parameters are considered.     

Investigation about the hot-carrier repelling effect in semiconductor devices, using an analytical solution of the hydrodynamic model

In this paper, the author discusses the consequences of the back-thermal diffusion of hot carriers, using an analytical solution of the hydrodynamic model (HDM). He observed a total deformation in the carrier distribution, around the reverse-biased semiconductor junctions, due to the back-thermal diffusion mechanism. At sufficient reverse bias, the diffusion of minority carriers (generation in neutral regions) is found to be influenced by the carrier-temperature gradient. Therefore, charge carriers are pushed forth (by electric-field effect) and back (by the thermal gradients) and the balance between these forces are controlled by the applied bias value. This may explain the origin of the terahertz oscillations in semiconductors after excitation by ultrafast laser pulses, which is currently an issue of debate. In order to confirm the validity of the proposed theory, the transport of hot carriers across a reverse-biased p-i-n diode is simulated using the HDM, and the conventional drift-diffusion model. He shows that the number of hot minority carriers is not at the junction boundary, but has an appreciable value, as if they are repelled back from the junction boundary to the cold neutral-region side, by thermal diffusion. He also proposes a simple analytical solution of the set of hydrodynamic equations, to demonstrate his theory of hot-carrier transport in semiconductor devices in general and across p-n junctions in particular. On the basis of his analysis, he discusses the terahertz generation from a reverse-biased p-i-n diode, which is subjected to femtosecond laser pulses.     

The effects of microwaves on airborne microorganisms.

This paper reports preliminary results of simple experiments carried out to study the effects of microwave irradiation at 2.45 GHz on fungi, yeast and bacteria of the type encountered in food processing plants or in enclosures containing individuals infected with tuberculosis mycobacterium (TB). The results are sufficiently encouraging to justify further multivariable experiments particularly with air circulation schemes in which the air can be sterilized in a circular cylindrical microwave cavity operating at a higher order mode.