Application of holography to the measurement of velocity gradients in fluid flows sensitized with photochromic dyes

A novel joint application of holography and photochromic materials to the experimental measurement of velocity gradients in a fluid flow is presented. A short study of some photochromic materials of interest is presented from the point of view of their applicability to experimental fluid mechanics. This includes a spatiotemporal model for the photoinduced conversion reaction which allows for optimization of the experimental conditions. The forced Rayleigh scattering method for measuring velocity gradients using photochromic materials is then briefly described and applied to the measurement of the velocity gradient in a boundary layer. Spatial resolution of 100 μm and gradient resolution of 3 sec−1 are obtained using these techniques.