Reflective layers

Layer Stacks and Protective Layers. The layer stack of an MO disk consists mainly of an MO layer, a dielectric antirefiection layer, and a metallic reflection layer (Fig. 14). The thickness of the antireflection layer as well as that of the MO layer have to be properly chosen to obtain a maximum magnetooptical figure-of-mefit (FOM). The FOM can be further increased by using a quadfilayer configuration with dielectric layers on both sides of the MO layer. Practical disks use the generalized configuration 50—120-nm dielectric layer, 25—90-nm MO layer, 17—70-nm dielectric layer (for quadfilayer configuration only), and 15—150-nm reflective layer. 

Spreading and reflective layer (Ti02 pigmented porous cellulose acetate coating)... 

In terms of processing there is no need for pre-drying PCHE granules, a standard extruder screw as used for polycarbonate may be used and discs are said to release well from the mould. Question marks remain on the oxidative stability of the polymer and on the quality of adhesion of the reflective layer but Dow claim that metallising is possible. 

This method was developed by Johnston et al. in 1991 and well described in Ref. [10], according to which the method is introduced as follows. The principle of optical interference is shown schematically in Fig. 1. A coating of transparent solid, typically silica, of known thickness, is deposited on top of the semi-reflecting layer. This solid thus permanently augments the thickness of any oil film present and is known as a "spacer layer. The destructive interference now obeys the equation ... 

The disk was coated with a 20 nm sputtered chromium semi-reflecting layer, a silica spacer layer was sputtered on top of the chromium. This spacer layer varied in thickness in the radial direction, but was approximately constant circumferentially round the disk [10]. 

A breakthrough came in 1988 when Hamada et al. demonstrated that a dye layer with a relatively low optical absorbance and high reflectance at the recording wavelength could be interposed between the substrate and reflecting layer of a CD-ROM type structure, and, with appropriate optimization of the optical properties, this would record and reproduce in accordance... 

Depending on the size of an incorporated dye, the angle of the transition dipole moment to the c axis lies between 0° for long molecules and 72° for smaller ones. Therefore, if a small molecule is inserted into the channels of zeolite L, part of the emission will be parallel to the c axis. Due to the flat and parallel ends of appropriately prepared zeolite crystals, one can envisage to arrange crystals between two mirrors or to add a reflecting layer on individual crystals. This might lead to a microlaser with a plane-parallel resonator. Apart from experimental difficulties, the realization of a dye-loaded zeolite L microlaser appears to be feasible. 

The second dye system is based on an almost clear yellow-green phthalocyanine dye. The estimated lifetime of a disc based on the phthalocyanine dye is 100 years. The third dye system is based on azo dyes. The azo dye used in the process has a deep blue color partially caused by its unique silver alloy reflective layer. Again, a projected lifetime of 100 years is cited. 

The two most widely employed reflective layers are 24 K gold and a silver alloy. The layers are thin enough, about 50-100 nm thick, to allow us to see through them. 

It is easy then to write down the oscillation condition for a dye laser. In its simplest form a dye laser consists of a cuvette of length L [cm], with dye solution of concentration m [cm-3], and of two parallel end windows carrying a reflective layer, each of reflectivity R, which form the laser resonator. With mi molecules/ cm3 excited to the first singlet state, the dye laser will start oscillating at a wavelength A if the overall gain is equal to or greater than one ... 

The reflectivity of the marks, (Rf — Rf, was measured as a function of pulse energy. At high pulse energies, the reflectivity saturates indicating that all the dye in polymer material is removed. Furthermore, the reflectivity of very large marks was approximately 90% (identical to that of the aluminum reflecting layer). The signal contrast, C, was therefore, as expected, equal to 0.7. 

The fluoroscopic screen consists of a substrate (cardboard, plastic sheet), which is first covered with a reflective layer of MgO or TiOz. The phosphor layer is applied by pouring, after dispersion in a binding agent based on acetylcellulose. 

Intensifying screens consist of cardboard or plastic sheets (e.g., polyester) as substrates. A reflective layer (e.g., TiOz) is first applied to this and then the phosphor-binder layer. 

Filter dyes are used to protect the silver halide while it is developing in ambient light. Dyes suited to this purpose are the phthaleins, such as compounds (77) and (78) which have Amax in potassium hydroxide solution at 470 and 620 nm, respectively. These dyes become colourless as the pH of the process is lowered to about 5-8 (72USP3702245, 72USP3702244). The titanium dioxide present in the activator fluid forms a white reflective layer needed for viewing the ultimate colour print. 

In addition to its function in catalysis, zinc often plays an important structural role, e.g., in the zinc finger transcriptional regulators (Fig. 5-38).k Zinc ions bind to insulin and stabilize its hexameric structure (Fig. 7-18)/ Six Zn2+ ions are present in the hexagonal tail plate of the T-even bacteriophage (Box 7-C) and appear to be essential for invasion of bacteria.131 In carnivores, the tapetum, the reflecting layer behind the retina of the eye of many animals, contains crystals of the Zn2+-cysteine complex. 

A characteristic feature of these partially oxidized bis(oxalato)platinate salts of divalent cations is the coexistence of two modulations of the lattice over a wide temperature range (a) a one-dimensional modulation, as detected by the appearance of diffuse lines on X-ray films, perpendicular to the [Pt(C204)2] anion stacking direction and surrounding the even Bragg reflection layer lines of non-zero order (b) a three-dimensional modulation which gives rise to a complicated pattern of fine satellite spots in the neighbourhood of every reciprocal layer line. 

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