White-light velocimetry

Abstract

RADIATION reflected from a moving object experiences a Doppler shift in its frequency. This basic phenomenon underlies practical interferometric techniques for remote velocity measurement used widely in meteorology and law enforcement, as well as in medicine1 (using acoustic waves) and other fields of science and engineering2–5. Existing velocimetric techniques use coherent quasi-monochromatic sources of illumination, which, for optical applications, generally limits practical sources to lasers operating in single-frequency mode. Such sources are not, however, sufficiently powerful for applications where simultaneous velocity measurements at many points on a target are desired. Here we describe a technique for remote velocity measurement that uses broadband incoherent illumination. The viability of this technique is demonstrated by measuring the velocity of a target moving at 16 m s−1 using white light from an incandescent source. Powerful, compact and inexpensive radiation sources (such as flash and arc lamps, or lasers operating at several wavelengths) can now be exploited for high-power applications of remote-target velocimetry.