Optical detection of terahertz phonon dynamics in disordered doped insulator systems using a new FLN-based technique

Abstract A new technique for the optical detection of nonequilibrium phonons in disordered solids is accomplished for the case of the strongly disordered crystal MgAl 2 O 4 :Cr 3+ and of Cr 3+ doped glasses with the help of site-selective laser excitation of dopant Cr 3+ ions within the inhomogeneously broadened 4 A 2 - 2 E transition (Δ v ≈150 cm -1 ) at liquid helium temperature. Nonequilibrium phonons, produced either by the heat pulse technique or in the course of electronic relaxation after optical excitation, are detected in the frequency range 5–100 cm -1 with both temporal and frequency resolution using phonon-induced anti-Stokes luminescence from the upper crystal field components of the 2 E-doublets of Cr 3+ ions excited resonantly into the lower 2 E-components at laser frequency v exc . The phonon-induced anti-Stokes luminescence kinetics at frequency v = v exc + ω reflect the kinetics of phonons with frequency ω in the excited volume.