Surface-illuminated systems

Light microscopy allows, in comparison to other microscopic methods, quick, contact-free and non-destmctive access to the stmctures of materials, their surfaces and to dimensions and details of objects in the lateral size range down to about 0.2 pm. A variety of microscopes with different imaging and illumination systems has been constmcted and is conunercially available in order to satisfy special requirements. These include stereo, darkfield, polarization, phase contrast and fluorescence microscopes. 

The Zeiss PMQ 3 chromatogram analyzer is probably the most versatile thin-film scanner available (Fig.3.13). The system can be used for reflectance, transmission, simultaneous reflectance and transmission and fluorescence quenching. It has two direct fluorescence modes, one with filter emission and surface illumination at a direction of 90° to the surface of the plate, and the other with 45° illumination and monochromatic emission. The instrument can be used for scanning thin-layer chromatograms, paper... 

Given the susceptibility of fused silica to laser-induced damage, particularly at high fluences at 193-nm wavelength, it is not used in the illuminator lenses. Rather, at present, calcium fluoride is used in most 193-nm illumination systems for elements where fused silica s lifetime has been projected to be unacceptably short. Also, when necessary, optical coatings that are laser resistant and can function as antireflection coatings are coated on fused silica lenses to protect them from surface damage. Typically, fused silica lenses are used in the projection optics where fluences are much lower than in the illuminator lenses. ... 

The triangulation approach is useful in the testing of threc-dimensioanl shapes to determine variations in depth by measuring scattered light from a surface illuminated by two overlapping spots [30]. Such systems have been developed to measure tire tread depth but suffer from poor resultion and dynamic range. For these reasons, laser based systems have been developed for improved precision and accuracy. 

Diamond machined optical components have conquered a huge market. They are needed for projection systems, displays, laser scanners, sensors, reflective tapes, scientific instruments, medical and defense equipment, laser beam guiding, and illumination systems exhibiting a multitude of different surfaces ranging from rotational symmetric aspheres to freeform and structured surfaces with Fresnel or prismatic elements (Table 3). Moreover, aspheric glass and plastic... 

One of the most critical aspects of observation using any optical microscope is the specimen illumination. Two illumination systems are commonly used in optical microscopy transmitted light and reflected light (Fig. 2). Transmitted, also called diascopic illumination, requires the specimen to be transparent. It is used primarily to examine thin sections of biological or material samples. Reflected light, or episcopic illumination (epi-illumination), is most commonly used for fluorescence microscopy, where fluorphores inside the specimen are excited to produce fluorescent light. The fluorescence is then emitted, or reflected back to the objective and collected by the detector (eyes, or camera). The reflected light is also used to study the surfaces of opaque specimens, which is the focus of this session. 

Laser projection systems have both a broader color spectmm and a higher lifetime compared to conventional illumination systems. However, lasers have the inherent problem of speckle on rough optical surfaces (e.g., a wall or a cinema screen), local interferences cause a grainy pattern of spots observable with a camera or naked eye. This effect causes noise in projected images but also reduces the resolution of measurement systems. 

Even in the absence of texture the HVS is able to reconstmct the shape of an object solely from self-occlusion induced shading. When interpreting shading, the visual system tends to assume objects to be convex, not concave, and fighting from above. To support the perceptual analysis, the object has to have a uniform and diffuse surface illuminated by a diffuse and uniform light soiuce. If these assumptions do not hold or the preconditions are not given, the interpretations based on shading alone are liable to be inaccurate. 

Fljring-spot instruments permit point-by-point analysis of surface properties. At first, it would appear that transmission electron microscopes, which illuminate an entire sample, would not be suitable for such an application, and in general, this is so. However, a new transmission electron microscope named EMMA 4 has been developed with combined transmission electron microscope and probe capability by introducing a minilens into the illumination system (Cook etal, 1969 Jacobs, 1971). The EMMA 4 has demonstrated eonsiderable power in a number of applications and could easily be applied to surfaees, but it will not be further considered here because our primary emphasis is on the topography of paint. 

Let us consider the scheme showed in Fig. I to calculate the field scattered by a rough cylindrical surface (i.e. a wire). The wire is illuminated by a monochromatic, linearly polarized plane wave at an angle of incidence a with its axis of symmetry. The surface is described, in a system fixed to the wire, by p = h (cylindrical coordinates. We shall denote the incident wave vector lying on the x-z plane as kj and the emergent wave vector simply as k. 

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