A new acoustic phonon spectrometer

Paramagnetic impurities which interact primarily with the resonant phonons in a dielectric crystal and show large magneto-optical properties can be used as a tunable and sensitive probe of the acoustic waves, or phonons, in a dielectric crystal. Such a technique usually works only at a few degrees Kelvin and is tunable over a wide frequency range, 10-500 GHz, with a magnetic field.