Direct visualization of phonon-polariton focusing and amplitude enhancement

We report a new method to generate focused phonon polaritons inside ferroelectric crystals. Using an excitation pulse in the form of a ring we generate a phonon-polariton wave packet that propagates inward toward a focal point at the center. This results in a sharp increase in the polariton intensity. It also permits direct visualization and quantitative measurements of the Gouy phase shift and of anisotropy in polariton propagation. Since vibrational and electromagnetic modes are coupled, coherent vibrational amplitudes can be increased substantially through exploitation of electromagnetic wave propagation. (C) 2002 American Institute of Physics.