8. Conclusion and outlook

The use of tracers to investigate fluid movements is still very much in vogue, despite the fact that it has been around for several centuries. There's no doubt that the advent of coherent optics in the 1970s gave it a new lease of life. Within two decades, the use of sheets of light became the norm, due to the three-dimensional nature of tomographic analysis; but its success is also largely due to the fact that it is easier to implement for non-optical experimenters, and more flexible to use, even in harsh environments, than the optical methods presented in [ .