Schlieren photography is based on the acousto-optic
effect [1–5] and is important when ultrasound is to be
visualized [6–10]. In a Schlieren experiment, a wide
beam of coherent laser light propagates through a transparent
medium in which ultrasound propagates. The
presence of sound generates a light-diffraction grating
which is caused by the spatially periodically varying
refractive index which in its turn is caused by traversing
soundwaves. Hence light is diffracted into several spatial
orders [1–5]. Since only orders different form zero deviate
from light that is not diffracted, the zero order field
must be eliminated in order to visualize the presence ofsound by means of the diffracted light. The obtained
light is then projected on a screen and can be used to
visualize ultrasound.
However, if an inhomogeneity in the refractive index
is present due to other effects, it may also be visible on a
Schlieren picture. The visualization of heat often occurs
in other scientific areas by means of Schlieren photography
as well [11–16]. Nevertheless, as far as we know, the
simultaneous visualization of sound and sound induced
heat, has not been reported yet.