PARTICLE IMAGE VELOCIMETRY - IMAGE LABELING USING ENCODING OF THE POINT-SPREAD FUNCTION BY APPLICATION OF A POLARIZATION-SENSITIVE PUPIL MASK

A method of labeling the first and second exposure particle images of a double-exposed particle image velocimetry (PIV) recording using a si ngle-wavelength, double-pulsed laser is demonstrated. This was achieve d by rotating the polarization plane of the second pulse of the illumi nating laser beam using a Pockels cell in conjunction with a polarizat ion-sensitive adaptive optic placed close to the iris plane of the pho tographic camera objective. This system effectively changed the transf er characteristics of the recording optics between exposures, producin g two sets of particle images modulated by orthogonally oriented fring es. The particle images that correspond to each exposure were then sep arated by digital spatial filtering. This permitted the individual par ticle fields to be cross correlated to yield unambiguous displacement vectors. The technique can be applied to any flow in which the seeding particles retain the incident polarization plane in side scatter. The advantages and disadvantages of such a system compared with conventio nal PIV recording are discussed.