Laser fluorescence velocimeter.

A new technique is described in which fluid flow velocity can be determined using the laser-induced fluorescence (LIF) signal produced by a space and time modulated excitation. The modulated excitation is produced by a crossed-beam probe volume similar to those commonly employed in particle-scattering laser Doppler velocimeters (LDV). The technique relies on a flow-induced variation of the visibility and phase of the fluorescence signal that results from the finite lifetime for fluorescence decay of the excited species. A simple, infinite reservoir model is presented to illustrate the technique and to identify the controlling parameters.