Filling of an optically created phonon void

Abstract A local frequency-selective depletion of phonons is realized in a single crystal of dilute ruby at 1.8 K by optical pumping into the Zeeman-split metastable E ( 2 E) doublet. This phonon void, which is in dynamic balance with the spin system, is filled by an inward flow of phonons ultimately supplied by the helium bath. A quartic frequency dependence for phonon transport across the crystal-helium interface is found, in accordance with diffuse phonon scattering at the crystal surface.