Focal Curves

Color Plate 23 Polychromator for Inductively Coupled Plasma Atomic Emission Spectrometer with One Detector for Each Element (Section 21-4) Light emitted by a sample in the plasma enters the polychromator at the right and is dispersed into its component wavelengths by grating at the bottom of the diagram. Each different emission wavelength (shown schematically by colored lines) is diffracted at a different angle and directed to a different photomultiplier detector on the focal curve. Each detector sees only one preselected element, and all elements are measured simultaneously. [Courtesy TJA Solutions, Franklin, MA.J... 

Fig. 4.4(a) A series of ellipses of increasing "homogeneity" (variation of curvature), and a circle, together with their respective focal curves (also called "evolutes"). The focal curve for the homogetteous case, the circle, degenerates to a single point at the circle s centre. 

Fig. 33) seen in smectic A phases. Focal curves and translation dislocations are not excluded from fan textures. The fan patterns themselves can be absent from certain arrangements of disclinations, which however belong to the family of fan textures. This is illustrated by the rhombus in Fig. 34 a and b, where two -i- r and two -tt disclinations are associated with several focal curves at the top and bottom levels of the mesophase. 

As indicated above and illustrated in Fig. 32 i, layers lie horizontally in planes and show some translation dislocations. They are oblique in polygonal fields and generally cross the focal lines at points where they are strongly hat-shaped, whereas elsewhere they are saddle-shaped and dislocations are present, often superimposed on the focal lines. In fans, the layers are vertical and all types of defect (disclinations, focal curves, dislocations) are present. 

Figure 37. Model of the arrangement of layers and io" e ferroelectric display can be focal lines in the texture shown in Fig. 36. (a) Distri- smoothed by focal curves and Other defects,...

All the expressions given above for discli-nation and focal curve energies are similar to those for screw and edge dislocations in true crystals [9,15], but the situation is different for translation dislocations in smectics. The presence of a screw dislocation of weak Burgers vector does not introduce any splay and does not really modify the layer thickness even at small distances [16]. The energy is reduced to a core term and therefore interaction terms are absent in the frame of the linear theory. This is not the case for edge dislocations in this approximation [106], and one has the expression ... 

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