|Date||April 11, 2012||Time||4:00 - 5:00 pm|
|Location||Baylor Sciences Building, Room E.125|
Professor, Texas A&M University
Dancing in Unison: Emergence of the Optical Coherence from Chaos
Synchronization in an ensemble of weakly coupled oscillators is one of the most fascinating phenomena in nature. It has been observed in a variety of systems: from atoms to chemical reactions, neurons, and genetic circuits. In rare cases the process occurs spontaneously, starting from initially incoherent oscillations with random relative phases, and results in a macroscopic coherent state. In optics, emergence of the optical coherence yields an added bonus: a bright outburst of coherent light. After general introduction to the subject, we discuss several examples of self-organization in a very unlikely system: dense electron plasma, created in a semiconductor crystal by current or light pulse. Electrons in semiconductors are like tiny electromagnetic oscillators that can emit or absorb light by jumping between energy levels in the bands. However, they also bump into each other or into the ions of a crystal lattice. Their coupling to light is many orders of magnitude weaker than scattering that tends to destroy coherence between individual particles. Nevertheless, we found that under certain conditions myriads of these nano-antennas can self-synchronize to form a giant macroscopic optical antenna, which emits a powerful, extremely short burst of coherent radiation, called superfluorescence. A different kind of self-synchronization occurs in semiconductor lasers, where individual oscillators are electromagnetic modes of a laser cavity. Their phases are random, and one can synchronize them by imposing periodic modulation of some laser parameter. To our surprise, we found that recently discovered quantum cascade lasers could exhibit spontaneous self-synchronization, which emerges as a bifurcation and results in the generation of frequency combs and ultrashort pulses: a holy grail for laser applications.
For More information, please contact: Dr. Anzhong Wang x 2276
|Publisher||Department of Physics|
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