3. Tomographic methods

A mechanically optimized tracer is useless if it cannot be easily detected by the light it emits.

In this respect, the size criterion is antagonistic to dynamic behavior: a submicron tracer, ideal for tracking changes in fluid direction or acceleration, does not always diffuse a recordable quantity of light; only a careful analysis of lighting and diffusion conditions can enable a compromise to be chosen. For quantities of tracers that are small enough to remain undisturbed, only the power density of a laser light can enable easily exploitable observation. This idea gave rise to the principle of distributed "sheet" illumination, obtained by spreading a laser beam using an optical system originally consisting of a simple cylindrical glass rod [16] . At the same time, a decisive advantage of light sheeting...