Optical data disc

PMMA has not been able to compete in the field of compact discs, the market having gone to the polycarbonates (see Chapter 20). It is, however, suitable for optical data storage using large video discs. Large-scale acceptance in the field of optical fibres has been held back by problems of obtaining material of an acceptable level of purity. 

Heat. As mentioned above most molecules lose energy from the excited state as heat. The most efficient molecules for converting electromagnetic radiation into heat are those that absorb in the near-IR region, i.e., infrared absorbers (IRAs). There has been much interest in IRAs because of their use in laser thermal transfer, optical data storage [the older write-once read-many (WORM) and the newer compact disc recordable (CD-R) and digital versatile disc recordable (DVD-R) systems], computer-to-plate printing, and as solar screens for car windscreens and windows. 

Dithiolene complexes, and more specifically the nickel derivatives, are involved in materials used for optical data storage, such as compact disc or laser disc read-only memory (CD- or LD-ROM), and also in copiers or photography related devices. In the latter case, it is the IR-absorbing property that is exploited. Some of these compounds can be found in reviews by Mueller-Westerhoff et al. (353, 354). Recent patents are given as examples in references (458—481). In the field of optical storage, short reviews were published in 1988 (482) and 1990 (362, 483). Here, the dithiolene complexes act as inhibitors of the laser-induced fading of the colored thin layers of the optical discs. They also act as an antioxidant and increase the photostability of the cyanine dyes that constitute the recording layer. Contrary to what was observed for the two... 

The high optical damage threshold, low dielectric constants, hi photosensitivity, and low cost of photorefractive polymers make them more efficient than inorganic materials (129). Optical data storage in PMMA-based photorefractive polymers has been demonstrated as a cheap and compact way improve data stoi age on compact discs and digital versatile discs (103). Polysiloxane-based photorefractive polymers have demonstrated the highest optical clarity and lowest optical scattering to date (105). 

The storage and retrieval of data by optical means, which involves the interaction of some medium with a compact laser, focused to sub-micron size, is dominated by direct bit storage onto disc media. The various types of storage media, from read only compact discs (CD-ROM) to rewritable digital versatile discs (DVD-RW), and the favoured recording materials are shown in Figure 4.5. ... 

As the name implies, liquid-crystalline materials combine the properties of a crystal with those of a liquid in a very special way and are therefore of interest for display and data storage technology. Liquid-crystalline compounds usually consist of rod- or disc-shaped organic molecules which preferentially adopt a mutually parallel orientation [33]. A change of molecular orientation caused by application of an electrical potential transforms the optical properties and can be utilised for display applications. 

Figure 4.8. Schematic representation of the pressure-jump apparatus of Davis and Gut-freund (1976). The instrument is composed of the following components A, observation cell B, hydraulic chamber C, absorbancy photomultiplier D, thermostatted base E, quartz fiber optic from light source F, quartz pressure transducer for the triggering of data collection G. hydraulic pressure line H and I, observation cell filling and emptying ports J, fluorescence emission window K, bursting disc pressure-release valve L, mechanical pressure-release valve M, trigger mechanism N, reset mechanism O, value seat and P, phosphorbronze bursting disc. (Reprinted with permission of the publisher.)...

This report will discuss the results of a study in which an optical multichannel analyzer (OMA) was coupled to standard spectrometers to record both the UV/VIS absorption and fluorescence emission spectra of complex mixtures of PAH s separated by HPLC techniques "on-the-fly" (i.e., one second spectral scans of the HPLC effluent stream) and stored on a floppy disc for subsequent retrieval and data analysis. The system described has the capability of storing 250 (500 point) spectra and can readily be used to increase the effectiveness of HPLC analysis by allowing both quantitative and qualitative data to be obtained. 

Optical Multichannel Analyzer System (OMA 2). The OMA 2 system consisted of a PARC Model 1215 console, two PARC Model 1254 SIT detectors, two PARC Model 1216 detector controllers, and a PARC Model 1217 flexible disc drive. The SIT detector is controlled by the 1216 detector controller, which provides both power and scanning voltages and processes the signal for transmission to the OMA 2 console. The OMA 2 console performs all necessary control functions, data acquisitions, data processing and storage of spectra. The system can store 250 (500 points) spectral curves when equipped with the Model 1217 flexible disc drive. 

In the years since the introduction of the first CD, the lasers and other hardware have changed significantly. We now have read-only memory discs (CD-ROMs) for the optical storage of many different kinds of data, CDs for our computers that we can... 

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