A Polychromator chip that combines diffractive optics and microelectromechanical systems (MEMS) is envisioned as a key building block for new remote sensing devices that would enable users to determine the composition of gas clouds from as far as two miles away. Now being developed by Sandia National Laboratories -- in a joint effort with Honeywell Inc. and the Massachusetts Institute of Technology -- the Polychromator chip offers a major advantage over conventional correlation spectroscopy methods, since it eliminates the need for cells containing reference samples of the various gases to be detected. The new chip -- about the size of a dime -- could be incorporated into binoculars carried by soldiers in chemical-warfare situations, allowing them to detect toxic gases from a safe distance. The technology also has "many possible commercial applications," says Mike Sinclair, a Sandia researcher who developed a computer program to design the diffraction grating profiles formed on the chip. Among the possibilities: enabling regulatory agencies to remotely monitor gas emissions from industrial plants or permitting firefighters to quickly determine whether the fumes from a blaze pose a serious hazard. The Polychromator chip consists of thousands of MEMS diffraction grating elements -- slivers of silicon 10 microns wide. As infrared light from a gas cloud strikes the chip, the gratings move up and down, creating various spectral patterns corresponding to different gases. When a match occurs, the voltage output from the detector alerts the user to the presence of a specific gas. Remote sensors employing the chips conceivably might check for 20 different gases in about 20 seconds, Sinclair estimates. Fully functioning prototypes aren't expected, however, until 2001. John Teresko, John Sheridan, Tim Stevens, Doug Bartholomew, Patricia Panchak, Tonya Vinas, Samuel Greengard, Kristin Ohlson, and Barbara Schmitz contributed to this article.