Light reflected

Figure Bl.18.10. Scaimmg microscope in reflection the laser beam is focused on a spot on the object. The reflected light is collected and received by a broad-area sensor. By moving the stage, the object can be scaimed point by point and the corresponding reflection data used to construct the image. Instead of moving the stage, the illuminating laser beam can be used for scaiming.

Kim Ki H, So P T C, Kochevar I E, Masters B R and Gratton E 1998 Two-photon fluorescence and confocal reflected light imaging of thick tissue structures Proc. SPIE 3260 46-57... 

The intensity of the reflected light must also be measured. Historically, this was done using the eye. Since, in general, a null (a measurement of the point at which the light decreases to zero) is required, this can be relatively sensitive. However, nowadays, the light intensity is generally measured using a photomultiplier tube. 

This is the Reflected Light Melting Point Apparatus " marketed by Townson sind Harcar Ltd., Croydon, Englsind. 

Refra.ctive Index. The relative amount of light reflected by a surface is dependent on both components of the iaterface, ie, filler and air. The refractive iadex is a measure of a substance s tendency to reflect light according to Fresnel s equation ... 

Gloss, or surface luster, is the property of a surface to reflect light specularly. It is associated with such phenomena as shininess, highlight, and reflected images. The gloss of paper is usually quantified with a spectrophotometer which measures light at a variety of angles of incidence and reflection. 

Measurement of Whiteness. The Ciba-Geigy Plastic White Scale is effective in the visual assessment of white effects (79), but the availabihty of this scale is limited. Most evaluations are carried out (ca 1993) by instmmental measurements, utilising the GIF chromaticity coordinates or the Hunter Uniform Color System (see Color). Spectrophotometers and colorimeters designed to measure fluorescent samples must have reversed optics, ie, the sample is illuminated by a polychromatic source and the reflected light passes through the analy2er to the detector. 

Fig. 2ab. Photomicrographs of foam cell stmcture (a) extmded polystyrene foam, reflected light, 26 x (b) polyurethane foam, transmitted light, 26 x (c) polyurethane foam, reflected light, 12 x (d) high density plastic foam, transmitted light, 50x (22).

Consumer Products. Laser-based products have emerged from the laboratories and become familiar products used by many millions of people in everyday circumstances. Examples include the supermarket scaimer, the laser printer, and the compact disk. The supermarket scanner has become a familiar fixture at the point of sale in stores. The beam from a laser is scaimed across the bar-code marking that identifies a product, and the pattern of varying reflected light intensity is detected and interpreted by a computer to identify the product. Then the information is printed on the sales sHp. The use of the scanner can speed checkout from places like supermarkets. The scanners have usually been helium—neon lasers, but visible semiconductor lasers may take an impact in this appHcation. 

The compact disk player has become a very widespread consumer product for audio reproduction. The information is stored along tracks on the disk in the form of spots of varying reflectivity. The laser beam is focused on a track on the surface of the disk, which is rotated under the beam. The information is recovered by detecting the variations in the reflected light. The compact disk offers very high fideHty because there is no physical contact with the disk. This appHcation has usually employed a semiconductor laser source operating at a wavelength of around 780 nm. Tens of millions of such compact disk players are produced worldwide every year. 

A similar effect occurs in highly chiral nematic Hquid crystals. In a narrow temperature range (seldom wider than 1°C) between the chiral nematic phase and the isotropic Hquid phase, up to three phases are stable in which a cubic lattice of defects (where the director is not defined) exist in a compHcated, orientationaHy ordered twisted stmcture (11). Again, the introduction of these defects allows the bulk of the Hquid crystal to adopt a chiral stmcture which is energetically more favorable than both the chiral nematic and isotropic phases. The distance between defects is hundreds of nanometers, so these phases reflect light just as crystals reflect x-rays. They are called the blue phases because the first phases of this type observed reflected light in the blue part of the spectmm. The arrangement of defects possesses body-centered cubic symmetry for one blue phase, simple cubic symmetry for another blue phase, and seems to be amorphous for a third blue phase. 

Fig. 3. Design of topover diagnostic coatings, where and represent the initial and reflected light intensities, respectively.

The TSM can be modified for reflected light confocal microscopy (TSRLM). In that case, one Nipkow disk above the objective serves both for the illuminating beams and the reflected image-forming rays. 

Direct photography of drops in done with the use of fiber optic probes using either direct or reflected light. StiU or video pictures can be obtained for detailed analysis. The light transmittance method uses three components a light source to provide a uniform collimated beam, a sensitive light detector, and an electronic circuit to measure the amplified output of the detector. The ratio of incident light intensity to transmitted intensity is related to interfacial area per unit volume. 

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