Dark-field reflected light

Oscilloscope traces from a line scan across the dark field reflecting light images were used to determine the amount of dispersion in a quantitative manner. However, this technique is not capable of evaluating details of the structure of the dispersed phase. 

In general, images may be formed in reflection in similar ways to those used in transmission. Thus bright-field [8], dark-field, polarised light [20] and... 

Figure 2.4 (Upper) White-light (polarized) photomicrograph, in reflected mode, of an suspension with a significant emulsified oil content. With polarized light, the clays (C) appear bright, but the oil droplets cannot be seen at all. (Lower) In this reflected-light photomicrograph, of the same field of view as above, the fluorescence mode shows bright oil droplets in a dark water-continuous phase. In this photograph the clays cannot be seen. From Mikula [66], Copyright 1992, American Chemical Society.

Another optical version of a microscope is called the darkfield microscope. This microscope has proven to be particularly useful for biological studies. The dark-field microscope uses a specialized illumination technique that capitalizes on indirect illumination to enhance contrast in specimens. An opaque disk is set in a condenser under the stage of the microscope (the solid support that the object being studied rests on). The disc is also known as the stop. The stop prevents light from shining directly on the specimen. Instead, light passes around the stop and is reflected off the condenser s walls. 

Figure 1.29 Dark-field illumination in a reflected light microscope.

This is because the initial condition of vapor deposited or electroplated films can be very smooth. A semiquan-titative measure of roughness is provided by the intensity of the light reflected by a scunple examined under a microscope with dark field illumination. Data taken by this technique is shown in Figure 3. The pronounced dependence of attack on RH is very clear in this exan le. Roughening is much more severe at high RH than at low. 

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