Abstract: An optical device having a variable index of refraction across its surface includes a light transmissive material with a plurality of regions in the light transmissive material. Each region has an index of refraction which is different from the remainder of the material. The regions may be arranged in the surface of the material such that the density of the regions on the surface varies across the surface. Each region may be a bore, including a hole that extends through the light transmissive material. Variations in the density of the regions or bores as well as the depth and shape of the bores may be utilized to create variations of the refractive index within the light transmissive material. The regions form a refractive lens.

Abstract: An optical device having a variable index of refraction across its surface includes a light transmissive material with a plurality of regions in the light transmissive material. Each region has an index of refraction which is different from the remainder of the material. The regions may be arranged in the surface of the material such that the density of the regions on the surface varies across the surface. Each region may be a bore, including a hole that extends through the light transmissive material. Variations in the density of the regions or bores as well as the depth and shape of the bores may be utilized to create variations of the refractive index within the light transmissive material.

Abstract: A directionally sensitive, high contrast secondary electron detector having a novel geometrical configuration for use in scanning electron microscopes and other electron beam instruments. The aperture of the detector which is placed near the specimen is in non-parallel arrangement with the aperture which admits the primary beam. The geometry of the detector provides for tilting of the specimen with respect to the incident primary electron beam to improve sensitivity and signal-to-noise ratio in comparison with prior detectors. In the preferred embodiment, the shape of the upper grid of the detector is substantially that of a conic section, thereby preventing space-charge build-up during operation.