Abstract. Compact aplanatic concentrators can reconstitute the flux of a near-field ultrabright incoherent light source and couple it into an optical fiber. Performance near the thermodynamic limit for light transfer can be realized, even at high numerical aperture. The prospect of arc-discharge lamps as alternatives to lasers for many surgical fiber-optic procedures motivate this investigation. LED-fiber and fiberfiber coupling constitute additional applications. The contours of these achromatic mirrored systems are analytic functions, which facilitates rapid surveying of a wide range of design options. Aplanatic optics that are compact and perform near the thermodynamic limit were recently developed for solar concentration ͑far-field sources͒ as well as collimation ͑with the roles of source and target reversed͒.1 Here, these solutions are generalized to the near-field problem, with illustrations of flux performance for practical applications. The motivation stems in part from the need to efficiently reconstitute the ultrabright radiant region in short-arc discharge lamps 2-4 into an optical fiber, such as required for photothermal surgery, 5,6 and, more generally, whenever a sizable gap between source and concentrator is imposed.Additional applications include LED-fiber or fiber-fiber coupling. Conventional imaging devices are adequate when the numerical aperture ͑NA͒ of both source and target is small. The challenge lies in the realm of high NA, heightened by polychromatic sources because contoured refractive elements incur chromatic aberration. Accordingly, our illustrations comprise high-NA, pure-reflective optics.The strategy is to tailor two mirror contours to eliminate spherical and comatic aberration. While the source and target NA can be chosen at will ͑even NA= 1͒, imposing constraints such as low shading and blocking considerably narrows the range of admissible solutions. Figure 1 depicts the near-field problem: tracing a ray emitted at arbitrary angle from point source O within NA 1 = sin͑ max ͒ to focus F at angle within target NA 2 = sin͑ max ͒. Aplanats satisfy Fermat's principle of constant optical path length ͓Eq. ͑1͔͒, as well as the Abbe sine condition, constant magnification m ͓Eq. ͑2͔͒:Now add Snell's law and specify the distances between: ͑a͒ the source and the apex of the primary ͑ o ͒; ͑b͒ the vertices of the primary and secondary ͑l o ͒; and ͑c͒ the focus and the apex of the secondary ͑r o ͒. Only two of these three lengths are needed since the third establishes the dimensional scale. Head 7 proved that the solutions for the primary and secondary mirrors, ͑͒ and r͑͒, are analytic:

Electropolishing is a widely-used electrochemical surface finishing process for metals. The electropolishing of stainless steel has vast commercial application, such as improving corrosion resistance, improving cleanness, and brightening. The surface topography characterization is performed using several techniques with different lateral resolutions and length scales, from atomic force microscopy in the nano-scale (<0.1 µm) to stylus and optical profilometry in the micro-and mesoscales (0.1 µm-1 mm). This paper presents an experimental length scale study of the surface texture of ground stainless steel followed by an electropolishing process in the micro and meso lateral scales. Both stylus and optical profilometers are used, and multiple cut-off lengths of the standard Gaussian filter are adopted. While the commonly used roughness amplitude parameters (Ra, Rq and Rz) fail to characterize electropolished textures, the root mean square slope (RΔq) is found to better describe the electropolished surfaces and to be insensitive to scale.

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Recycling light back into a plasma lamp's radiant zone can enhance its radiance. Measurements are reported for the effectiveness, spectral properties and modified plasma radiance maps that result from light recycling with a specular hemispherical mirror in commercial 150 W ultrabright Xenon short-arc discharge lamps, motivated by projection, biomedical and high-temperature furnace applications. For certain spectral windows and plasma arc regions, radiance can be heightened by up to 70%. However, the overall light recycling efficiency is reduced to about half this value due to lamp geometry. The manner in which light-plasma interactions affect light recycling efficacy is also elucidated.

During a program's runtime, the stack and data segments of the main memory often contain much redundancy, which makes them good candidates for compression. Compression and decompression however require either extra hardware or substantial processing resources. This paper presents a new approach in which a mostly software solution is suggested but without the processing power penalty that usually accompanies such a solution. This is achieved by not compressing all the memory all of the time. The suggested method is to identify the current working set and to leave it uncompressed for faster access. Pages that are not in the working set may be compressed during the CPU's idle time. Also, compression is only performed during phases which exhibit good spatial locality. These phases are identified by detecting changes in the program's working set. By comparing the current working set's "signature" with the signature at the end of the previous instruction window, a difference parameter is calculated and, when the difference is low enough, the program is in a phase that exhibits good locality and thus compression may begin. Simulation results confirm that this new approach to main memory compression provides good compression ratios for most SPEC CPU2000 programs.