coondoggie writes to mention that a new optical technique for sensing small amounts of molecules in a person's breath has been developed by a researcher for the National Institute of Standards and Technology. The goal is to create a fast, low-cost method for detecting disease. "In this approach, NIST researchers analyze human breath with 'frequency combs,' which are generated by a laser specially designed to produce a series of very short, equally spaced pulses of light. Each pulse may be only a few million billionths of a second long. The laser generates light as a series of very narrow frequency peaks equally spaced, like the teeth of a comb, across a broad spectrum."