  We report on the direct measurements of fluid flow vorticity using a
spatially shaped beam with a superposition of Laguerre-Gaussian modes that
reports on the rotational Doppler shift from microparticles intersecting the
beam focus. Experiments are carried out on fluid flows with well-characterized
vorticity and the experimental results are found to be in excellent agreement
with the expected values even for 200 ms integration times. This method allows
for localized real-time determination of vorticity in a fluid flow.
