Impulsive generation of coherent hybrid modes by light pulses.

Coherent terahertz-frequency hybrid modes in solid state materials are studied by subpicosecond pump-probe experiments. Near-infrared optical pulses are used to generate, control, and detect coherent oscillations of various types. A stable phase-sensitive setup for transmission pump-probe experiments based on a Sagnac interferometer is developed. The amplitude of the impulsive stimulated Raman scattering signal from this phase-sensitive technique is compared to that of the conventional spectrally-filtered technique, and it is shown to be more sensitive for oscillations whose frequencies are significantly lower than the pulse bandwidth. Cherenkov radiation emitted by optical rectification of optical pulses is studied in highly dispersive media by spatially-resolved electro-optic sampling experiments. Coupling of terahertz radiation to the lattice results in a phonon polariton, and the strong dispersion results in a qualitative change in the Cherenkov radiation pattern. These experiments also demonstrate that impulsive excitation of phonon polaritons is analogous to electro-optic Cherenkov radiation in a dispersive medium, no matter the pulse shape. Calculations of terahertz radiation generated by optical rectification, based on the theory of Cherenkov radiation, allow one to easily include dispersion effects. Finally, hybrid intersubband-cyclotron oscillations in a two-dimensional electron gas are studied. In a modulation-doped semiconductor quantum well, electrons are trapped in a thin layer of GaAs and behave as a two-dimensional system. Pump-probe experiments in a magnetic field tilted with respect to the quantum well plane show coherent hybrid intersubband-cyclotron oscillations, collective modes of the electrons in which in-plane and cyclotron motions are mixed.PhDCondensed matter physicsOpticsPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125247/2/3186781.pd