Fibre-optic transit velocimetry using laser diode sources

Optical fibre laser velocimetry: a review

“…Velocity measurement techniques using the time-of-flight method measure a particle's time-of-flight between two known positions to determine the velocity. This can be done at a single location in the flow field, as in laser-two-focus (L2F) velocimetry [38][39][40][41], where a particle's transit time between two beams is measured, or at multiple locations using PIV and particle tracking velocimetry [42], where the motion of particles or groups of particles between the recording of two consecutive images with a known time separation is used to determine the velocity. Recently volumetric measurements have been demonstrated by various techniques using PIV [43].…”

“…The laser transit anemometer (LTA) or L2F anemometer [38][39][40] relies on the timing of the passage of a seeding particle between two tightly focused beams in the flow region. The beam diameters are typically around 10 μm with a spacing of 0.5 mm between beams.…”

“…The use of tightly focused beams allows signals to be obtained from small seeding particles, which follow high speed flows more faithfully. Finally the short measurement volume allows measurements to be made near surfaces, where the light scattered from the solid surface would introduce significant signal to noise problems for LDV configurations [39].…”