Propagation of ballistic phonons in crystals and their detection with a detachable bolometer

Ballistic phonons were generated in single-crystalline sapphire samples by scanning the crystal surface with the electron beam in a scanning electron microscope equipped with a low-temperature stage. The phonons were detected using a superconducting thin film (granular Al) bolometer configuration which could be detached from the sample crystal (allowing repeated use). We have applied these experimental techniques for obtaining phonon images of laser-drilled holes in the sample crystals, achieving a spatial resolution of better than 10 m.