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This book is the result of two decades of research work which
started with an accidental observation. One of my students, Dipl.
phys. Volkmar Lenz, - ticed that the speckle pattern of laser light
scattered by a cuvette containing diluted milk performed a strange
motion every time he came near the cuvette with his thumb. After
thinkingabout this e?ect we came to the conclusion that this motion
can only be caused by scatteringparticles with di?erent velocities,
as in the case of the di?raction pattern of an optical grating: A
linear motion of the grating does not change the pattern whereas a
rotation of the grating does. The observed speckle motion could
then be explained qualitatively as produced by the inhomogeneous
velocity of the convection within the cuvette which was produced by
the heat of the thumb. The theoretical treatment of this e?ect
revealed that the velocity gradient of the light scattering medium
is responsible for the speckle motion. The idea to use this e?ect
for developingmeasurement techniques for velocity gradients arose
almost immediately. For that purpose we had to develop not only
experimental set-ups to measure the pattern velocity but also the
theory which describes the connection between this velocity and the
velocity gradient. The result of this work together with the
description of a method developed by another group forms the
contents of this book. I am indebted to the students who worked in
my laboratory and developed the measurement techniques. These were,
in temporal order, Dr.
This book is the result of two decades of research work which
started with an accidental observation. One of my students, Dipl.
phys. Volkmar Lenz, - ticed that the speckle pattern of laser light
scattered by a cuvette containing diluted milk performed a strange
motion every time he came near the cuvette with his thumb. After
thinkingabout this e?ect we came to the conclusion that this motion
can only be caused by scatteringparticles with di?erent velocities,
as in the case of the di?raction pattern of an optical grating: A
linear motion of the grating does not change the pattern whereas a
rotation of the grating does. The observed speckle motion could
then be explained qualitatively as produced by the inhomogeneous
velocity of the convection within the cuvette which was produced by
the heat of the thumb. The theoretical treatment of this e?ect
revealed that the velocity gradient of the light scattering medium
is responsible for the speckle motion. The idea to use this e?ect
for developingmeasurement techniques for velocity gradients arose
almost immediately. For that purpose we had to develop not only
experimental set-ups to measure the pattern velocity but also the
theory which describes the connection between this velocity and the
velocity gradient. The result of this work together with the
description of a method developed by another group forms the
contents of this book. I am indebted to the students who worked in
my laboratory and developed the measurement techniques. These were,
in temporal order, Dr.
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