Data holograms.

Faced with a deluge of data -- the ever-growing mountain of information brought on by the ubiquitous computer -- researchers keep searching for ways to store lots of information in small spaces.

One route involves turning data into holograms.

Three Stanford University faculty members -- physicist John F. Heanue and electrical engineers Matthew C. Bashaw and Lambertus Hesselink -- have devised an information storage and retrieval system that records digital data holographically. Their report appears in the Aug. 5 SCIENCE.

The researchers achieve holographic storage by merging a laser beam carrying a picture with a so-called reference laser beam. The combination causes an interference pattern.

As the intensity of the interference pattern varies, a photosensitive recording material captures the signal. Once charged, the recording material's ability to refract light changes. "When the medium is exposed to a reference beam identical to the one used in recording, the light will diffract in such a way as to reproduce the original image," they explain.

A device called a spatial light modulator converts data into an optical signal for storage, they add. A hologram corresponding to one "data page" is then recorded in a special photoreiractive crystal. By changing the angle at which the image is "written," or recorded, the system can store multiple holographic images.

To read the data, the reference beam illuminates the crystal, which reflects an image onto an array of charged coupled devices that converts the picture into an electronic signal.

The system works for both color pictures and video images, the researchers explain. In one case, they viewed, recorded, and accurately retrieved a holographic image of Leonardo da Vinci's "Mona Lisa."