Microscopy, polarized illumination

Fig. 5.21 (a, b) Polarized dark-field opti d microscopy images of metallic nanoarrays. Arrows indicate the directions of polarized illumination, (c) Scetttermg light intensities from metallic nanoarrays as a function of the angle between the arrays and the polarization. The angle is 0° when the illumination polarization is parallel to the arrays. Reprinted with permission from [109]. Copyright (2010) by the Japan Society for Analytical Chemistry... 

This method describes the collection and analysis of asbestos bulk materials by light microscopy techniques including phase- polar illumination and central-stop dispersion microscopy. Some terms unique to asbestos anaiysis are defined beiow ... 

Polarized light microscopy This illuminates the sample with linearly or circularly polarized light, either in a reflection or transmission mode. One polarizing element, located below the stage of the microscope, converts the illumination to polarized light. The second polarizer is located between the objective and the ocular and is used to detect polarized light... 

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 structure (e.g., number, size, distribution) of fat crystals is difficult to analyze by common microscopy techniques (i.e., electron, polarized light), due to their dense and interconnected microstructure. Images of the internal structures of lipid-based foods can only be obtained by special manipulation of the sample. However, formation of thin sections (polarized light microscopy) or fractured planes (electron microscopy) still typically does not provide adequate resolution of the crystalline phase. Confocal laserscanning microscopy (CLSM), which is based on the detection of fluorescence produced by a dye system when a sample is illuminated with a krypton/argon mixed-gas laser, overcomes these problems. Bulk specimens can be used with CLSM to obtain high-resolution images of lipid crystalline structure in intricate detail. 

Figure 1.41 Optical arrangement of Nomarski microscopy in reflected light illumination. 1, polarizer 2, j-piate 3, DIC prism 4, objective lens 5, specimen 6, light reflector and 7, analyzer.

Van der Loos CM, Becker AE (1994) Double epi-illumination microscopy with separate visualization of two antigens a combination of epi-polarization for immunogold-silver staining and epi-fluorescence for alkaline phosphatase staining. J Histochem Cytochem 42 289-295... 

The SNOM combines the possibilities of AFM and optical microscopy. On the one hand, it allows for probing of the surface and obtaining information on the topography. On the other hand, in aperture SNOM, the probe contains an aperture, and the sample can be illuminated locally (Fig. 5). The diameter of the aperture at the end of the probe is typically of the order of 50-100 nanometer, and therefore, the illuminating spot is not diffraction limited. Both transmission and tluorescence in combination with polarization provide appropriate contrast mechanisms. 

Then, microscopic examinations follow optical research microscopes allow to determine the number, thickness, and color sequence of layers in paint fragments, and to recognize the textures as well as fundamental features of pigment and extender mixtures. Bright field and dark field illuminations, polarized light microscopy (incident and transmitted), particularly the differential interference contrast (DIC) procedure, and fluorescence microscopy are necessary for paint examinations (see Figure 3(A)-3(E)). 

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