  Many experiments in liquid Helium, such as the optical imaging of exploding
electron bubbles, which enables research on individual particles under applied
conditions, involve the usage of ultrasound generated by piezoelectric
transducers. Previous studies either use planar transducers, which limits the
maximum sound intensity and the spatial resolution, or curved transducers,
which only allow observations at fixed foci and make it difficult to apply
uniform electric fields. In this paper, we introduce the usage of acoustic
diffraction plates in liquid Helium to amplify ultrasonic pressure oscillations
at an arbitrary set of primary foci coupled with large counts of secondary
foci, all of which can be freely moved around by changing the ultrasound
frequency. The frequency dependence also allows us to generate controlled
Faraday instabilities at the surface, which enables the generation of
multi-electron bubbles with desired parameters.
