Optical materials crystalline quartz

Optical retarder plates, of appropriate thicknesses, made of birefrin-gent material, normally crystalline quartz or mica, can be used to rotate the plane of polarization for linearly polarized light or to produce circularly polarized light. To rotate linearly polarized light by an arbitrary angle, a double Fresnel rhomb is very useful (Fig.6.46). 

Microstructures and systems are typically fabricated from rigid materials, such as crystalline silicon, amorphous silicon, glass, quartz, metals and organic polymers. Elastomeric materials can be used in applications where rigidity is a drawback. We have demonstrated the concepts of elastomeric systems by fabrication of photothermal detectors, optical modulators and light valves. We believe that elastomeric materials will find additional applications in the areas of optical systems, micro analytical systems, biomaterials and biosensors. 

In practice, a convenient range of solid crystalline materials, which can be polished to optical flatness over manageable areas, exists and includes silicon, quartz, and sapphire. The equivalent transmission through a block of amorphous quartz or silicon is 10—15%. This has so far precluded them from use, and limited the application to crystalline substrates. In aqueous solution, the most commonly use contrasts are D20, H20, and water (H20/D20 mixture) index matched to the solid phase. In D20, the refractive index (or scattering length density) difference between that and the solid phase is significantly different for silicon, quartz, and sapphire (see Table 1). 

In general the optical activity exhibited by a crystal will persist in other states of aggregation only if it is due to the asymmetry of the finite molecule or complex ion. In this case it is also necessary that the energy of activation for racemization (change d 1) must exceed a certain value ( 80 klmol" at room temperature). The optical activity cannot, of course, be demonstrated unless there is a means of resolution (separation of d and / forms) or at least of altering the relative amounts of the two isomers. The optical activity of many crystals (e.g. quartz, cinnabar, NaC103) arises from the way in which the atoms are linked in the crystal it is then a property of the crystalline material only. 

Silica, the main component of silicates, is widely used as mentioned earlier. In its crystalline and noncrystalline polymorphs, silica is used industrially as a raw material for glasses, ceramics, foundry molds, in the production of silicon, and more recently in technical applications such as quartz oscillators and optical waveguides for longdistance telecommunications. Of the crystalline forms, only a-quartz is commonly used as sand or as natural and synthetic single crystals. Cristobalite is often utilized as the synthetic phase in glass-ceramics. 

Colorless amorphous (i.e., fused silica) or crystalline (i.e., quartz) material having a low thermal expansion coefficient and excellent optical transmittance in far UV. Silica is insoluble in strong mineral acids and alkalis except HE, concentrated HjPO, NH HE, concentrated alkali metal hydroxides. Owing to its good corrosion resistance to liquid metals such as Si, Ge, Sn, Pb, Ga, In, Tl, Rb, Bi, and Cd, it is used as crucible container for melting these metals, while silica is readily attacked in an inert atmosphere by molten metals such as Li, Na, K Mg, and Al. Quartz crystals are piezoelectric and pyroelectric. Maximum service temperature 1090°C... 

The transformation of P-quartz to P-spodumene is possible between 900 C and 1000°C. The irreversible procedure always entails the enlargement of the crystallites. As a result, the optical properties are often affected and the transmissibility decreases. Furthermore, if T1O2 is used as a nucleating agent, crystalline Ti02 forms as rutile. This crystal phase is known to demonstrate a high refractive index, which gives the material an opaque appearance. 

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