Nonlinear optical data storage

The application of nonlinear optical recording techniques for reversible optical data storage based on the excitation of photochromic molecules by two-photon processes also has been described (154). 

Polymers and supermolecules modified using electron push-pull chro-mophores are also of particular interest for nonlinear optics (NLO) [10-15]. NLO material has attracted much interest over the past 20 years and has been widely applied in various field (telecommunications, optical data storage, information processing, microfabrication, etc.). Chemists have developed ways to introduce NLO chromophores into many type of polymers, such as Hnear polymers, cross-linked polymers, and branched polymers, and have demonstrated their performance in NLO appHcations. 

By the sol-gel-process, inorganic glassy and hybrid polymeric materials are accessible at comparatively low temperatures [1], Therefore, organic molecules or dyes can easily be incorporated into the oxide matrix. This combination is especially attractive for the development of the following devices optical filters, solid-state lasers, optical switches, nonlinear optical laser hosts, optical data storage media, and photoconductive devices and films [2]. 

The chapters cover the following areas (i) use of coordination complexes in all types of catalysis (Chapters 1-11) (ii) applications related to the optical properties of coordination complexes, which covers fields as diverse as solar cells, nonlinear optics, display devices, pigments and dyes, and optical data storage (Chapters 12-16) (iii) hydrometallurgical extraction (Chapter 17) (iv) medicinal and biomedical applications of coordination complexes, including both imaging and therapy (Chapters 18-22) and (v) use of coordination complexes as precursors to semiconductor films and nanoparticles (Chapter 23). As such, the material in this volume ranges from solid-state physics to biochemistry. 

Other dye-based technologies evaluated for optical data storage include photo-chromic dyes for rewritable systems and azo dyes for holographic data storage. Spirobenzothiopyran dyes such as (40) absorb in the red/near-IR in their colored form and are suitable for erasible optical data storage [34]. Dyes for holographic data storage, such as (41), are similar to those used in nonlinear optics [35] (see below). 

Frequency Doubling. As the name implies, in frequency doubling a substance doubles the frequency of the incident laser radiation. This effect is important in telecommunications and optical data storage. For example, in telecommunications the most efficient way to transmit data is by using infrared radiation, e g., 1200 nm radiation from an indium phosphide laser [60], Detection of infrared radiation is inefficient. In contrast, visible radiation is much easier to detect but is an inefficient transmitter of data. Consequently, an important application of nonlinear optical (NLO) materials is to convert infrared radiation into visible and thus enable easier detection of the signal. 

Finally, in Section IV dithiolene complexes with interesting optical properties, such as strong near-IR (NIR) absorption, nonlinear optical behavior, and the use of some dithiolene complexes for optical data storage will be reviewed. In Section V, attempts toward coupling conducting, and magnetic or optical properties will be discussed briefly. 

Since Chapter 6 (352) in this volume is devoted to the luminescence and photochemistry of dithiolene complexes, these aspects will not be developed here. In this section, we restrict ourselves to the review of dithiolene complex-based compounds exhibiting optical properties, such as strong infrared (IR) absorption and second- and third-order nonlinear optical properties. In the last part of this section, we will review the use of some dithiolene complexes for optical data storage (printers, developer, CD-ROM, etc.). Contrary to what was observed throughout the two previous sections, no particular dithiolene complex really dominates the domain of the molecular materials exhibiting interesting optical properties. 

B. H. Cumpston, J. W. Perry, and S. R. Marder, Method and Apparatus for Optical Data Storage Using Nonlinear Heating by Excited State Absorption for the Alteration of Preformatted Holographic Gratings, 2001, US 6322931. 

Due to possible utilization of photo-induced orientation in polymeric films in optical data storage, this phenomenon and the quadratic nonlinear optical effects were extensively investigated in the last few years. It was reported, for instance, that to study photo-isomerization in a polymeric environment. 

Due to possible utilization of photoinduced orientation in polymeric films in optical data storage, this phenomenon and the quadratic nonlinear optical effects were extensively investigated in the last few years. It was reported, for instance, that to study photoisomerization in a polymeric environment, a series of polymers containing azo dyes with large differences in the second order transition temperature were compared. Particular emphasis was placed on the relationship between photoisomerization, Tgof the polymers, and their molecular structure. As a result, it was shown that light-induced nonpolar orientation in very high Tg polyimides (Tg up to 350 °C) can take place even at room temperature. The polymers used in one of these studies can be illustrated as follows... 

Nowadays most colorants have the purpose to satisfy our aesthetical needs and, thus, thousands of dyes and pigments are produced on industrial scales. Nevertheless, nearly periodically new demands arise for so-called fimctional dyes whose tt-conjugated systems exhibit novel functionahties beyond aesthetical purposes. Optical brighteners or near-infrared absorbers are examples where even transparency in the visible spectrum is desired and dyes for nonlinear optics, holographic optical data storage and two photon absorption are further examples where the color properties of dyes are insignificantly related to the functional demands. 

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