  Using the concept of an ideal phase-conjugating mirror we demonstrate that
regardless of internal physical mechanism the phase-conjugation of a singular
laser beam is accompanied by excitation within the mirror of internal waves
which carry doubled angular momentum in order to match angular momentum
conservation. For a Brillouin hypersound wavefront-reversal mirror this means
that each elementary optical vortex belonging to a speckle pattern emits an
acoustical vortex wave with doubled topological charge. The exact spatial
profiles of light intensity and the intensity of hypersound in the vicinity of
the phase singularity are obtained. These spiral profiles have a form of double
helix which rotates with the frequency of sound. An optoacoustic experiment is
proposed for visualization of the wavefront reversal of twisted optical beams
and tunable twisted sound generation.
