Fibre-optic beam delivery systems for particle image velocimetry

The role of fibre-optics in the formation of light sheets for particle image velocimetry is reviewed, concentrating on the power handling capacities of fibres and their effect on laser beam quality. It is shown that when continuous wave lasers are used, chopped to form a pulsed light sheet, then it is feasible to use a single multimode optical fibre to deliver the beam. Conversely, with Q-switched lasers, the peak power densities are so high that to achieve an adequate compromise between pulse energy and beam quality, delivery systems based on bundles of multimode fibres have been developed.