Number 142 (Story #1), September 1, 1993 by Phillip F. Schewe and Ben Stein TIME-DOMAIN OPTICAL MEMORY is a technique for storing multiple bits of information at a single location in a crystal. This technique, developed by Thomas Mossberg, now at the University of Oregon (503-346-3791), exploits the fact that molecules in crystals absorb and radiate light at many different frequencies, and has the potential of storing 1 million bits in a one-cubic-micron spot in a crystal. This corresponds to 100,000 atoms per bit--as opposed to the 50 trillion atoms per bit required for conventional data storage. To write information, a series of laser light pulses (constituting a binary message) burns a "spectral hole" at a tiny spot in a crystal. To read the information, a second series of pulses causes the crystal's molecules to radiate a frequency pattern identical to that of the first pulse. Recently, Ravinder Kachru (415-859-3727) of SRI International in California wrote 1,600 bits to a single 100-micron spot in a crystal. With a few advances in technology, it may be possible to store 50 million bits in the spot and read the information at a blazingly fast rate of 40 billion bits per second. However, practical crystalline materials must still be found for this technology. (Scientific American, September 1993.)