Illumination systems

The illumination system of a microscope provides visible light by which the specimen is observed. There are three main types of electric lamps used in light microscopes  

Back Focal Plane Objective Lens Specimen Condenser Lens Aperture Diaphragm 

The functions of the illumination system include (i) spectral filtering, (ii) establishing a specified level of spatial coherence, (iii) controlling the exposure dose, and (iv) providing uniform radiation to the mask. How the illumination system performs the above functions is briefly discussed below. 

The illumination system comprises a series of relay optics and uniformizing optics that project the radiation from the source through the photomask to the entrance pupil of the projection optics of the lithographic lens, where it forms an image of the illumination source (see Fig. 13.8). This type of illumination system is referred to as Kohler illumination. The fraction of the pupil filled by the illuminator source s image determines the degree of coherence in the projection 

Semperez, Excimer lasers for future lithography hght sources, Solid State TechnoL, pp. 255 260 (July 2000). 

Kahlert, U. Rebhan, P. Lokai, and D. Basting, Comparison of 248 nm hne narrowing resona tor optics for DUV htbograpby lasers, Proc. SPIE 1463, 604 609 (1991). 

The radiation traversing the entire chain of illuminator and projection optics forms an aerial image of the mask that is projected onto the resist-coated wafers. A fast shutter within the illuminator assembly exposes the photoresist to the image for a very short period of time, on the order of a few tenths of a second. The integrated energy of each exposure must he repeatable to within 1%, such that the illumination of the reticle is fairly uniform ( +l%) over a large area, a feat it accomplishes with the aid of a number of methods, including the use the of fly s eyes and rods.  

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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. 

Figure Bl.18.1. Light rays and imaging lenses in the microscope. The illumination system is not included.

The smallest resolvable stnicture is thus addition, the aperture of the illumination system... 

Figure Bl.18.4. The most frequently used illumination system in bright-field mieroseopy.

As the beam travels down the column, a number of electromagnetic lenses are used to guide the beam to the sample [44], The condenser lenses are part of the illumination system and are used to deliver electrons from the electron gun crossover to the sample. The condenser lenses determine the beam current reaching the sample. The objective, or final, lens determines the final spot size of the beam. A set of scanning coils are also present in the instrument column to scan the beam in a raster pattern over an area of the sample. At each point, data is collected and the points are combined to form the image. More detail on the data collection is given in the image formation section. 

IEJR Heynderickx and DJ Broer, Illumination System for a Color Projection Device and Circular Polarizer Suitable for Use in Such an Illumination System, and Color Image Projection Device Comprising Such an Illumination System and Circular Polarizer, U.S. Patent 5,626,408, 1997. 

The shape of the modulation vs. frequency curve for a given NA and wavelength is dependent on the degree of spatial coherency Kohler illumination and critical illumination, shown in Figures 19a and b respectively. With Kohler illumination. 

Figure 19. Two common types of illumination systems (a) Kohler, (b)...

Figure 6.16 Diagram of the dark-field illumination system used to visualise colloidal particles in water.

An illustration of the illumination used in this type of apparatus, to observe the motion of colloid particles, is given in Figure 6.16. Basically, the illumination system and microscope allow you to observe the motion of the silica particles, which are seen as bright star-like objects on a green background. When an electric field is applied the average time taken for the particles to travel a distance of one square on the eyepiece graticule can be easily measured. One particle is measured each time the field is applied for a short time (i.e. 10-20 s) and the polarity is then reversed and the speed in the opposite direction measured. The... 

Rapid prototyping (or stereolithography or 3D object curing) is a photochemical process used to produce solid 3D objects such as models, masters or patterns of any shape, directly from a design generated on a computer. The computer is used to control the illumination system that builds up the object, usually by a rapid polymerization process. An important part of the design is that the object is sectioned... 

The fluorescent light from the sample is observed at right angles to the illuminating system. It is passed through colored glass or interference filters or a combination of both. This permits the selection of the lines or group of lines to be observed. Filters of sufficient bandwidth are usually... 

When the non-polymerizable acceptor, CH3CN, is used instead of AN, the polymerization of VCZ is again very photosensitive. Although thermal polymerization is too slow to obtain accurate rate measurements, the mechanism is mostly cationic since the yield of polymer is not affected by oxygen and DPPH whereas ammonia and water retard polymerization. The illuminated system seems to be a mixture of cationic and radical polymerization. The effect of ammonia shown in Fig. 3 provides support for a duality of propagation mechanisms. 

Industrial-type Hazards—-with the objective of identifying hazard sources in electrical, mechanical, illumination, and non-emergency communication fields. Developments have included (a) advanced remote surveillance and communication systems, (hi portable-area illumination systems. Ic) trolley-phone wireless systems, and (d) protective canopies for use on underground low-coal machines. 

Dark-field illumination is a particularly useful technique for detecting the presence of, counting and investigating the motion of suspended colloidal particles. It is obtained by arranging the illumination system of an ordinary microscope so that light does not enter the objective unless scattered by the sample under investigation. 

When intercomparisons between results obtained by these two illumination systems were made, no significant differences were noted. Therefore, the rotary photoreactor (7) was used in the large majority of these studies. 

When 8-bit microprocessor-based computers became available, we decided that such a computer, even though slower than minicomputers, would be adequate to operate the OMA and our interface controller with the ultracentrifuge. We now have in the system an Altair 8800 computer with 28K of memory (MITS, Albuquerque, NM), a hard-wired arithmetic board and two minifloppy disk drives (North Star, Berkeley, CA), a 700 ASR Terminal (Texas Instruments, Dallas, TX), and a 7202A Graphic Plotter (Hewlett-Packard, Palo Alto, CA). Appropriate software, written in Basic, has been developed to collect intensity data from the OMA automatically and also to treat and plot the data at the end of the experiment. Details of the system and software will be published elsewhere. We also have an improved illumination system with a 200 W Hg-Xe arc lamp and a Model H-20 monochromator with a holo-... 

This is clearly seen in the plot of the data projected onto the first two principal components. Figure 6.15a shows the training data. In this figure, the cultivar D is marked with crosses, cultivar M with circles, and cultivar HA with diamonds. We see that cultivar HA has a cluster of outliers that are far from the other observations. As it turns out, these outliers were caused by a change in the illumination system. 

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