Optical alignment flats

Thin sheets of mica or polymer films, which are coated with silver on the back side, are adhered to two cylindrical quartz lenses using an adhesive. It may be noted that it is necessary to use an adhesive that deforms elastically. One of the lenses, with a polymer film adhered on it, is mounted on a weak cantilever spring, and the other is mounted on a rigid support. The axes of these lenses are aligned perpendicular to each other, and the geometry of two orthogonally crossed cylinders corresponds to a sphere on a flat surface. The back-silvered tbin films form an optical interferometer which makes it possible... 

The module further comprises a flat end surface 124 to which a substrate 126 may be bonded. The substrate is of alumina or sapphire and has disposed thereon a mosaic array 3 of electro-optical detectors 4. The detectors are formed by etching or laser cutting of a mercury cadmium telluride layer which has been deposited on the substrate. Each detector is connected at one end 130 to a common reference terminal 132 and at the other end 136 to terminal 134. The substrate further comprises a pattern of through holes 138 and metal dots 140 such that each signal terminal 134 contacts a dot 140. The substrate 126 is aligned on the end surface 124 such that the metal dots 140 in each hole 138 contacts a conductor 114. As a result, each detector 4 is coupled to a pad 118. 

Figure 3.11 An acoustic interferometer of the type used in the author s laboratory (from Nethery [104]). A X-cut quartz crystal, 100-600 KHz B crystal support mount and aligning screws. Optical flat E is attached to a movable reflector D for generation of ultrasonic standing waves. Invar rod F position is read from precision micrometer slide L.

Each sample has its own independent interferometer associated with it. A 5 mW red HeNe laser [Spectra Physics] is used as the energy source for the four interferometers that are in the system. The incident beam is split twice in order to provide incident beams to each of the independent interferometers. Each interferometer consists of a 50/50 beamsplitter, four mirrors [including two mirrors at 45°under the reactor to direct the beam into the reactor], and a beam expander in addition to the sample and reference mirrors located in the reactor. All of the optics have a flatness specification of X/10. The mirrors which make up the interferometer components outside of the reactor are enhanced aluminum. The 45° mirrors have adjustment screws so that the sample and reference beams can be aligned from outside the system once a run is started. 

The result obtained has very interesting consequences (i) to have well aligned SmA samples, very flat glasses without corrugation are needed (ii) even small dust particles or other inhomogeneities create characteristic defects in the form of semispheres (see Fig. 8.29b below) and weU seen under an optical microscope (iii) layers are often broken (not bent) by external factors in particular, strong molecular chirality may result in the formatimi of defect phases like twist-grain-boimdary phase (iv) the thermal fluctuations of director in smectic A phase are weak and the smectic samples are not as opaque as nematic samples. In fact there is a critical cell thickness for short-wave fluctuations. 

Optical fibers must often be joined, either permanently or temporarily, with minimal coupling loss and back-reflectiom Depending on the performance required, one of three methods are commonly employed to join optical fibers (1) fusion splicing, (2) mechanical splicing, or (3) butt-couphng mechanically aligned fibers terminated with cormectors. The flber ends to be joined must be clean, accurately aligned, and cleaved or polished, so the fiber end-faces are flat and parallel to each other. 

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