Memory, optical

Photochromic films based on phenoxynaphthacenequinone were characterized by high stability to irreversible phototransformations, in contrast to recording media with photochromic phenoxyanthraquinones. The above films allowed more than 500 cycles of rewriting of optical information at the same site of the light-sensitive layer. In addition, they were characterized by an extremely low rate of thermal relaxation from ana-quinoid into para-quinoid form. This means that the lifetime of the photoinduced form in a polymer film in darkness was equal to many years. 

Whatever the nature of the polymeric matrix, the sensitivity of photochromic films based on phenoxynaphthacenequinones reached 10 cm2/J to UV irradiation and 1 cm2/J to visible irradiation. These values were measured for the photoinduced change of optical density at the maximum of the absorption band of the photoinduced form.61 

Photochromic films of this type are suitable for recording polarization holograms because of the Veigert effect and oriented photodichroism.63 

Polymers with photochromic phenoxynaphthacenequinone side groups were also used for recording holograms.49 

Studies of photochromism of phenoxynaphthacenequinones in polymolecular layers62,63 suggested the possibility of the development of reversible optical memory on optical disks for operative recording and processing optical information. 

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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). 

Fig. 21. Principles of optical memory card constmction (Laser Card) (163).

Table 5. Requirements on Substrate Materials for Optical Memories...

The acceptance of optical data storage iato the mass storage market, which is as yet exclusively dominated by magnetic systems, will be fundamentally boosted if optical drives and media are subject to uniform standards and become fully compatible, and multiuser drives are offered which enable the user to employ alternatively CD-ROM and EOD disks, and maybe WORM disks as well (and CD-R disks, respectively). A prerequisite, however, will be whether rewritable optical memories will use the MOR or the PCR process. This accord especially will be hard to reach. 

General Presentation, Laser Card (Optical Memory Card), Drexler Technology Corp., 1989. 

Magnetooptic Materials. The appHcation of magnetooptic effects to optical memory systems, such as for laser beam writing and magnetooptic read, has been the subject of much research. Magnetooptic storage media offer the potential of storing over 120 Mbit/cm of information without contact of the read/write head which would thus be very competitive to floppy disks and tape. 

Materials are also classified according to a particular phenomenon being considered. AppHcations exploiting off-resonance optical nonlinearities include electrooptic modulation, frequency generation, optical parametric oscillation, and optical self-focusing. AppHcations exploiting resonant optical nonlinearities include sensor protection and optical limiting, optical memory appHcations, etc. Because different appHcations have different transparency requirements, distinction between resonant and off-resonance phenomena are thus appHcation specific and somewhat arbitrary. 

There is another class of amorphous semiconductors based on chalcogens which predate the developments that have occurred in i -Si. Because their use has been limited, eg, to switching types of devices and optical memories, this discussion is restricted to the optoelectronic properties of i -Si-based alloys and their role in some appHcations. 

Maenosono, S., Dushkin, C. D., Saita, S. and Yamaguchi, Y. (2000) Optical memory media based on excitation-time dependent luminescence from a thin film of semiconductor nanocrystals. Jpn. J. Appl. Phys., 39, 4006- 12. 

Ogawa K, Kobuke Y (2009) Design of two-photon absorbing materials for molecular optical memory and photodynamic therapy. Org Biomol Chem 7 2241-2246... 

CD-R was something of a surprise invention as, in the late 1980s, most of the major manufacturers in the optical memory area were commercializing the non-standard and relatively expensive WORM media, while focusing their research and development efforts on erasable optical storage. It was also believed that a writeable CD-Audio/CD-ROM-compatible medium was not feasible, due to the high reflectivity needed to meet the CD standard as defined by the Red and Orange Books.196... 

Hampp, N. (2000) Bacteriorhodopsin as photochromic retinal protein for optical memories. Chemical Reviews, 100, 1755-1776. 

Ohta, T. 2001. Phase-change optical memory promotes the DVD optical disk. J. Optoelectron. Adv. Mater. 3 609-626. 

Optical lithography, in compound semiconductor processing, 22 193 Optically active citronellol, 24 506 Optically transparent porous gel-silica, 23 75, 76 Optical materials nonlinear, 17 442-460 second-order nonlinear, 17 444—453 third-order nonlinear, 17 453-457 Optical memory, photochromic material application, 6 602 Optical microscopy, 16 467-487 history of, 16 467-469 in kinetic studies, 14 622 liquid immersion, 15 186 Optical mode density, 14 849, 850-852 Optical multichannel analyzers (OMAs), 23 143... 

Technical Digest of papers presented at International Symposium on Optical Memory 1987, Tokyo, September 1987. 

S. Nespurek, Molecular optical memories and switches based on photochromic dihydropyridines, BioSystems, 27, 213-218 (1992). 

Photochromic dithienyl- and dibenzothienylethenes, particularly those containing the central 1,2-perfluorocyclopentene fragment, belong to the major group of compounds, which have attracted the attention of researchers in the field of information storage (optical memory) and optical switches because their starting (A) and cyclic (B) forms are, in most cases. 

Photochromic dendritic polymers 74 considered as optical memory elements were characterized (08CC5755). 

For a photochromic material to be of any use in optical memories it must meet the minimum requirements in the following physical properties ... 

Figure 1.15 Principle of 3D optical memory and a model photochrome.

The photodimer (Scheme 27) of acridizinium ethylhexanesulfonate has been used as a non-destructively read-reversible optical memory material to control the intensity and wavelength of emission from a laser (72MI21000). 

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