Coherent phonon avalanches
H. W. de Wijn, P. A. van Walree, and A. F. M. Arts
Faculty of Physics and Astronomy, and Debye Research Institute, Utrecht
University, P.O. Box 80.000, 3508 TA Utrecht, The Netherlands
Avalanches of resonant acoustic phonons are observed following population
inversion of the Zeeman-split E(2E) doublet in
dilute ruby by selective optical pumping. In confined geometries only a
single stage of stimulated emission is seen, whereas longer crystals form
an acoustic cavity allowing multiple passage of the phonon pulse through
the active zone. Coherent equations of motion for the lattice
displacement and the spin Bloch vector excellently account for these
results.