OPTICAL-DETECTION OF TERAHERTZ PHONON DYNAMICS IN DISORDERED DOPED INSULATOR SYSTEMS USING A NEW FLN-BASED TECHNIQUE

A new technique for the optical detection of nonequilibrium phonons in disordered solids is accomplished for the case of the strongly disordered crystal MgAl2O4:Cr3+ and of Cr3+ doped glasses with the help of site-selective laser excitation of dopant Cr3+ ions within the inhomogeneously broadened 4A2-2E transition (Δv≈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 2E-doublets of Cr3+ ions excited resonantly into the lower 2E-components at laser frequency vexc. The phonon-induced anti-Stokes luminescence kinetics at frequency v=vexc + ω reflect the kinetics of phonons with frequency ω in the excited volume. © 1990.