Physics Department Current Events
Tuesday, October 28, 2014
12:30 p.m., Marshak Science Building, Room 418N
Wednesday, October 29, 2014
4:00 p.m., Marshak Science Building, Room 418N
Charles M. Vest Distinguished University Professor; James R. Mellor Professor of Engineering
Department of Electrical Engineering and Computer Science
University of Michigan, Ann Arbor, MI
"Strong Coupling Phenomena in Semiconductor Microcavities"
The study of light-matter interaction in a solid-state microcavity has been of considerable interest for some time. Under conditions of strong coupling, the irreversible spontaneous emission process changes to a reversible and periodic exchange of energy between emitter and cavity mode in the form of Rabi oscillations. The degeneracy between emitter and photon is lifted, giving rise to two light-matter entangled eigenstates spectrally separated by a characteristic interaction energy, or Rabi splitting, ΩVRS. Elementary excitations in a strongly coupled exciton-photon system are quasiparticles called polaritons, which are bosons. A polariton laser, proposed in 1996, exploits the strong coupling regime of exciton-photon interaction in a microcavity. A degenerate and coherent state of polaritons is created near k// ~0 in the polariton dispersion by a combination of polariton-phonon, polariton-polariton, and eventually stimulated polariton-polariton scattering. The last process, which is phase coherent, is the principle gain mechanism. The coherent polariton state at k// ~0 generates coherent light by spontaneous radiative recombination. The separation of stimulation and emission results in coherent emission without the requirements of population inversion and with a much smaller level of excitation than in a conventional photon laser. The concept therefore represents a new paradigm in the history of coherent emission. The exciton binding energy and ΩVRS are important factors which determine the choice of materials. In this talk I will describe ultralow threshold optically excited room temperature polariton lasing with a single and array of GaN nanowires and electrically pumped polariton lasers with GaAs-and GaN-based microcavities.
Thursday, October 20, 2014
12:00 noon- 2:00 p.m., Great Hall, 2nd Floor, Shepard Hall
"Connection to a Major and/or Minor"
Pallab Bhattacharya, Charles M. Vest Distinguished University Professor; James R. Mellor Professor of Engineering, Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI