Optical reflexion

The area most commonly determined is that of "frustrated optical reflexion". Total reflexion occurs (in a range of incidence angles) when light reaches a body of a low refractive index from a body of a high index, for instance, when a light beam passes a polymer and is refracted... 

Optical Properties.—The refractive index of tantalum is 2-05, the coefficient of absorption 2-31, and the reflexion capacity 43-8 per cent, when measured with yellow light of wave-length A=5790.5 The spectral emissivity and the radiation intensity and their variation with temperature have been measured by Worthing.6 For a comparison of the radiation constants of tantalum, platinum, osmium and carbon, see the references cited.7 The flame spectrum of tantalum between carbon electrodes consists of a blue cone with a reddish-yellow edge.8... 

A Mylar film was contaminated with NaCl and dried in air before metallization. XPS profiles were carried out in different areas of these samples. Observations by optical microscope were also made in reflexion and transmission modes. 

Figure 3.4-2 a Approximate optical conductance of a grating spectrometer, an interferometer (R = 1000 at 1000 cm ) or a laser b cuvette of minimal volume for trace analyses of gases c multiple reflexion cell (White cell) d cell for liquids with minimal volume. 

Polarized incident radiation is necessary also when anisotropic samples such as stretched polymers (Flournoy and Schaffers, 1966) are studied. Crystals may require immersion in order to assure the necessary optical contact. Plastic selenium has proved to be useful (Gottlieb, 1968). In this way the three different infrared spectra of an orthorhombic single crystal were obtained which are shown in Fig. 2.7-10 (cf. Sec. 2.7.6.4 Schrader et al., 1971). The orientation of the optical axis or axes with respect to the experimental frame is crucial. For the evaluation the field components have to be considered separately in order to interprete the response of the oriented transitions correctly. Addressing different components equivalently is achieved by rotating the sample together with the internal reflexion element with respect to the beam (Hobbs et al., 1983 Palm, 1994). 

We shall first consider the propagation of light along the optic axis for wavelengths much smaller than the pitch so that reflexion and interference... 

If reflexions are neglected, the optical rotation per thickness P of the liquid crystal is and the rotatory power is given by (4.1.21). Near the... 

Absorbing systems the Borrmann effect The Borrmann effect is the anomalous increase in the transmitted X-ray intensity when a crystal is set for Bragg reflexion. An analogous optical effect in absorbing cholesteric media in the vicinity of the reflexion band has been predicted and confirmed experimentally. The origin of the effect can be readily understood by extending the dynamical theory to include absorption. However, in contrast to the X-ray case, the polarization of the wave field and the linear dichroism play an essential part. 

The theory of propagation inclined to the optic axis is, of course, very much more complicated, and analytical solutions have not so far been found. The first attempt at solving the problem numerically was by Taupin, but the most complete calculations are those of Berreman and Scheffer who also carried out a precise experimental study of reflexion from monodomain samples at oblique incidence. Fig. 4.1.15 presents their observed reflexion spectra for two polarizations. 

The first evidence that more than one form of smectic A exists came from an observation of Sigaud et of a phase transition that was detected by calorimetry, but could not be observed optically. X-ray studies revealed that this was a transition between two forms of the A phase the higher temperature phase was characterized by a pair of refiexions corresponding to a layer spacing and the lower temperature one by two pairs of reflexions corresponding to fi / and 21 respectively. The former type of smectic A is called the monolayer (A ) phase and the latter the bilayer (Aj) phase. A third type which has a layer spacing intermediate between / and 21, has been identified and is called the partially bilayer (A ) phase. The structures of these phases are represented schematically in fig. 5.6.1. 

Fig. 4.4. Block diagram of optical system for electronic absorption spectrophotometry. L, L, biconvex silica lenses M, Mi, multiple reflexion cell (eight traversals shown) N, deuterium arc P, Hakuto R106 photomultiplier cell Q, wavelength drum and marker (R) S, recorder T, Vibron electrometer amplifier, U, grating. (After ref. 60.)...

A NIR spectrometer system has been described based on optical fibres for absorption and reflexion measurements, an AOTF and a transputer system. It is able to detect 1,000 spectra per second and to identify 20 pieces per second (209). The identification system was implemented and tested for a real-world application of plastic identification in municipal solid waste. 

Generally there are two possibilities for the illumination of flows whereby the most common is the illumination with a light sheet perpendicular to the camera axis. Especially in microscale divices, e.g. microchannels, it is often not possible to generate a hght sheet with a thickness of a few micrometers because there is either no optical access or reflexions from the close-by wall disturb the optical path. For that reason the whole volume is illuminated and the measurement depth is defined by the depth of field of the optical setup. 

TEFLON AF 2400 is highly permeable to gases. It has a low refractive index, lower than water. This allows total reflexion using water as core in long path-length capillary cells. It is UV-transparent and very expensive. It is commonly used in tubing, membranes, windows, and optical libers used as flow cells. 

Molecules which do not have a center, a plane or a reflexion-rotation axis of symmetry, are optically active. The best example is the asymmetric carbon atom which has four different substituents. These molecules have some rotatory power, which is routinely measured in polarimetry by their ability to rotate monochromatic light (most often the D line of sodium at 589 run or 5893 A) after preliminary passage through a polarizing crystal. 

For many applications the pulse repetition rate f = c/2d (which is f = 150MHz for d = Im) is too high. In such cases the combination of syn-chroneous pumping and cavity dumping (Sect. 11.1.2) is helpful, where only every k-th pulse (k > 10) is extracted due to Bragg reflexion by an ultrasonic pulsed wave in the cavity dumper. The ultrasonic pulse now has to be synchronized with the mode-locked optical pulses in order to assure that the ultrasonic pulse is applied just at the time when the mode-locked pulse passes the cavity dumper (Fig. 11.15b). 

For opaque materials to visible light, as metals and some ceramic and polymeric materials, only the surface of the material can be observed. For this reason, the optical microscope should be used in the reflexion mode. The contrasts in produced image result from the differences in the reflectivity of several regions of the microstructure [26]. 

---