Chemists have made real advances towards the realization of three-dimensional optical data storage. Chemical and Engineering News (dyes that absorb two photons at infrared wavelengths and emit one photon at a higher wavelength. This is desirable because infrared lasers can penetrate more deeply into a medium than visible lasers. Using confocal scanning laser microscopy, Prasad and his group probed into a polymeric medium permeated with “APSS,” a dye, and were able to bleach the dye at very precise points in the medium.

The exact chemistry of the bleaching isn’t clear, but it could be due to a cis-trans isomerization about the central double bond (shown in color above). These chemists were, in this way, able to write photobleached images into a polymer cube in well-defined planes separated by about five micrometers. (One micrometer is one millionth of a meter.) When the medium is subsequently scanned across a given plane with the infrared laser, two-photon absorption by unbleached dye molecules “lights up” the plane; the previously bleached dye molecules appear as a dark image. Rapid scanning of the different planes can produce an animation. The degree of photobleaching can be controlled so that images of varying darkness can be produced.In other work, University of California, Irvine chemists led by Peter Rentzipis embedded two absorbing molecules, 1-nitro-2-naphthaldehyde and Rhodamine-B (a dye), uniformly throughout a polymer matrix. The molecules absorb light at different wavelengths. When the two are irradiated simultaneously with both wavelengths of light, the simultaneous absorption by the two different molecules causes a light-induced (photochemical) reaction between them that produces a deeply-colored fluorescent product. In this way, a fluorescent image can be produced at a point by focusing the two laser beams at the point. Information is thus stored in very precisely defined planes within the polymer medium. The medium can be “read” by monitoring the fluorescence of the product; fluorescence indicates a “written bit.” Using this technique, data equivalent to several hundred compact discs can be stored in a 1-cc cube of polymer. In other words, more than 100 gigabytes of data can be stored in a cube that is about one-half inch on an edge!

In other work, University of California, Irvine chemists led by Peter Rentzipis embedded two absorbing molecules, 1-nitro-2-naphthaldehyde and Rhodamine-B (a dye), uniformly throughout a polymer matrix. The molecules absorb light at different wavelengths. When the two are irradiated simultaneously with both wavelengths of light, the simultaneous absorption by the two different molecules causes a light-induced (photochemical) reaction between them that produces a deeply-colored fluorescent product. In this way, a fluorescent image can be produced at a point by focusing the two laser beams at the point. Information is thus stored in very precisely defined planes within the polymer medium. The medium can be “read” by monitoring the fluorescence of the product; fluorescence indicates a “written bit.” Using this technique, data equivalent to several hundred compact discs can be stored in a 1-cc cube of polymer. In other words, more than 100 gigabytes of data can be stored in a cube that is about one-half inch on an edge!

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