Wednesday, February 23, 2011

TODAY: 2.23.11 / CREOL 102 / 11-12pm / Seminar: "Lasers,Anti-lasers and PT-symmetric Laser-Absorbers" - Dr. Stone

Seminar: "Lasers, Anti-lasers and PT-symmetric Laser-Absorbers" - Dr.

Stone

CREOL 102

Wednesday, February 23, 2011 / 11:00-12:00pm

Dr. A. Douglas Stone

Yale University

Abstract:

A laser is an optical device that transforms incoherent input energy (the pump), into coherent outgoing radiation in a specific set of modes of the electromagnetic field, with distinct frequencies. There is a threshold pump energy for the first lasing mode, and above that energy the laser is a non-linear device and non-linear interactions strongly affect the emission properties of the laser. Surprisingly, the theory of non-linear multimode lasing was quite rudimentary until recently. We describe a new formalism, based on non-hermitian states of the electromagnetic field, which provides a quantitative and tractable description of arbitrarily complex laser systems, including extremely open and non-linear examples, such as random lasers.

Our reformulation of laser theory emphasizes that a laser cavity is a certain kind of scattering system, with a non-unitary amplifying scattering matrix due to the presence of gain. This approach suggested the possibility of constructing a time-reversed or “anti-laser”, which we term a coherent perfect absorber (CPA); a device in which the gain medium of the laser is replaced with a loss medium such that the cavity will perfectly absorb the incoming

(time-reversed) modes of the corresponding laser. Recently we have experimentally demonstrated such a device in a simple silicon cavity, which acts as an absorptive interferometer, in which narrow-band absorption can be both increased to ~ 99% and reduced to ~30%. Finally, the same point of view leads to hybrid devices, containing both gain and loss media, which can function simultaneously as a laser and a perfect absorber for distinct modes of the electromagnetic field. This happens as a result of a spontaneous symmetry breaking transition, which destroys the parity-time-reversal symmetry of the eigenstates of the corresponding S-matrix.

For More Information:

Dr. Demetrios Christodoulides

407-882-0074

demetri@creol.ucf.edu

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