Ballistic heat pulses in crystals
The physics of phonons, or elastic waves, with gigahertz to terahertz frequencies is currently gaining considerable attention. A variety of new phonon techniques has been developed over the past few years as a result of new technologies and materials; they include notable advances in the generation of tunable monochromatic phonon beams at terahertz frequencies, in the creation of “phonon optics” devices such as reflection gratings for ultrasonic waves, and in the interaction of high‐frequency phonons with impurities and free carriers in semiconductors. This recent activity was particularly evident at the Third International Conference on Phonon Scattering in Condensed Matter held last year at Brown University.