  Irradiation with UV-C band ultraviolet light is one of the most commonly used
ways of disinfecting water contaminated by pathogens such as bacteria and
viruses. Sonoluminescence, the emission of light from acoustically-induced
collapse of air bubbles in water, is an efficient means of generating UV-C
light. However, because a spherical bubble collapsing in the bulk of water
creates isotropic radiation, the generated UV-C light fluence is insufficient
for disinfection. Here, we show that we can create a UV light beam from
aspherical air bubble collapse near a gallium-based liquid-metal microparticle.
The beam is perpendicular to the metal surface and is caused by the interaction
of sonoluminescence light with UV plasmon modes of the metal. We calculate that
such beams can generate fluences exceeding $10$ mJ/cm$^2$, which is sufficient
to irreversibly inactivate most common pathogens in water with the turbidity of
more than $5$ Nephelometric Turbidity Units.
