Recording medium, simplest

The simplest recording medium is a bilayer structure. It is constructed by first evaporating a highly reflective aluminum layer onto a suitable disk substrate. Next, a thin film (15-50 nm thick) of a metal, such as tellurium, is vacuum deposited on top of the aluminum layer. The laser power required to form the mark is dependent on the thermal characteristics of the metal film. Tellurium, for example, has a low thermal diffusivity and a melting point of 452 °C which make it an attractive recording material. The thermal diffusivity of the substrate material should also be as low as possible, since a significant fraction of the heat generated in the metal layer can be conducted to the substrate. For this reason, low cost polymer substrates such as poly (methylmethacrylate) or poly (vinyl chloride) are ideal. 

The simplest way of measuring the dispersion coefficient is to inject a well-defined volume of a dye solution into a colorless carrier stream and to monitor the absorbance of the dispersed dye zone continuously by a colorimeter. To obtain the value, the height (i.e., absorbance) of the recorded peak is measured and compared with the distance between the baseline and the signal obtained when the cell has been filled with the undiluted dye. Provided that the Lambert-Beer law is obeyed, the ratio of respective absorbances yields a value that describes the FIA manifold, detector, and method of detection. (An exercise dealing with dispersion measurements is given in Chapter 6, while examples of FIA systems using limited, medium, or large dispersion are described in detail in Chapter 4.)... 

The simplest case for the existence of an evanescent wave is the well-known total internal reflection of a plane electromagnetic wave at the base of a glass prism (index of refraction rii) in contact with an optically less dense medium (with ri2 < Hi), for example, air (Hj = ) This geometry is schematically sketched in Figure 4a (top). If the reflected light intensity is recorded as a function of the angle of incidence, 6, the reflectivity R reaches unity as one... 

Graven developed the use of DYLUX 503 proof paper, sold by DuPont as a medium for recording watermarks in the early 1970s. It is by far the simplest and least expensive technique and has thus been widely adopted. 

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