Gary Hieftje and Radislav Potyrailo of Indiana University in Bloomington have designed a "distributed" sensor that uses optical time-of-flight spectroscopy. The scientists operate the sensor by sending a very short pulse of light down the length of the fiber. (Currently in prototype form, the fiber measures 48 m.) When light interacts with an analyte, fluorescence propagates back down the fiber. Taking into account the velocity the light is traveling and the fiber's refractive index, scientists can determine where analytes are located along the fiber.