Optical disks

Data saving is realised on rewritable magneto-optical disks. Aftei field inspection, the complete datafile is... 

Optical Disk-Based Information and Document Image Systems... 

Depending on the method of data read-out, respectively read-in/read-out, two systems are distinguished mechanooptical systems with usually disk-shaped media (optical disks), and purely optical systems with card-shaped media without moving parts (optical memory cards). 

Erasable optical disk (EOD) systems, on the other hand, are challenging classic magnetic media in some areas of appHcation, primarily magnetic tape and the hard disk, but mostly optical media complement magnetic media. 

With disk diameters above 5.25 in., all parameters, eg, water absorption and thermal expansion, become more critical which aggravates the expansion or warp of disks. If in the future disk rotation speeds have to be increased significantly to boost data transfer rates, higher demands will be placed on warp (tilt angle) and modulus to avoid creeping (ie, irreversible elongation in radial direction). A survey of the requirement profile for the substrate material of optical disks is given in Table 5 (182,186,187,189). 

The distance between the disk surface facing the optics and the memory layer naturally has to be much smaller than in common optical disks, where the memory layer is deposited behind a 1.2-mm thick transparent glass or polymer substrate disk. 

Fig. 26. Qualitative compatison of substrate materials for optical disks (187) An = birefringence IS = impact strength BM = bending modulus HDT = heat distortion temperature Met = metallizability WA = water absorption Proc = processibility. The materials are bisphenol A—polycarbonate (BPA-PC), copolymer (20 80) of BPA-PC and trimethylcyclohexane—polycarbonate (TMC-PC), poly(methyl methacrylate) (PMMA), uv-curable cross-linked polymer (uv-DM), cycHc polyolefins (CPO), and, for comparison, glass.

Symmetrical, long-chain cyanine dyes for laser appHcations provide output from 680 to 980 nm (76). Although these dyes were obtained through early screening procedures, infrared dyes for other technologies use similar stmetures. A long-chain indolenine-type cyanine dye, general stmeture as in dye (34), has been described as the sensitizer in optical disk memories (77). 

Fig. 9. Examples of dyes used in optical disks. (14), pentamethine cyanine [36536-22-8] (1 )> nickel dithiene complex [38465-55-3] and (16) lR-810.

Optical functions are important both to transmit information through fiber optic cables and to store information on optical disks. An optical fiber... 

FIGURE 58-3. Normal fundus of the eye and optic disk and cup. (From FesarTS, Fiscella RG, Edward D. Glaucoma. In DiPiro JT, Talbert Rf, Yee GC, et al, (eds.) Pharmacotherapy A Pathophysiologic Approach. 6th ed. New York McGraw-Hill 2005 1715, with permission.)... 

In the reproducing (reading) process, the presence of the colorless form is detected by difference in reflectivity using the same laser beam at weak power (1 mW), and the signal is picked up by photodiode. In reversible process, the nonrecording area again was obtained by UV irradiation. Practically, in such optical disks using spirothiopyran, an S/N of 54 dB was detected.89-100... 

Corrosion of Magneto-optical Disks 7.1 FeTb and Alloys... 

Specific requirements for dyes for optical disk recording 609... 

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