  The generation of hydrodynamic radiation in interactions of pulsed proton and
laser beams with matter is explored. The beams were directed into a water
target and the resulting acoustic signals were recorded with pressure sensitive
sensors. Measurements were performed with varying pulse energies, sensor
positions, beam diameters and temperatures. The obtained data are matched by
simulation results based on the thermo-acoustic model with uncertainties at a
level of 10%. The results imply that the primary mechanism for sound generation
by the energy deposition of particles propagating in water is the local heating
of the medium. The heating results in a fast expansion or contraction and a
pressure pulse of bipolar shape is emitted into the surrounding medium. An
interesting, widely discussed application of this effect could be the detection
of ultra-high energetic cosmic neutrinos in future large-scale acoustic
neutrino detectors. For this application a validation of the sound generation
mechanism to high accuracy, as achieved with the experiments discussed in this
article, is of high importance.
