Klaers, Jan
Date: Monday October 27, 2014
Time: 15:00
Place: ETH Zurich, Hönggerberg, HPF G 6
Host: Atac Imamoglu
The thermalization, condensation and flickering of photons
Jan Klaers
University of Bonn, Germany
Other than in a three-dimensional thermal photon gas as Planck’s blackbody radiation, photons can exhibit Bose-Einstein condensation, if the thermalization process is restricted to two motional degrees of freedom. In experiments of our group, a two-dimensional photon gas is confined in a high finesse microresonator containing a dye medium. The cavity geometry imposes a quadratic energy-momentum relation on the photons, making them formally equivalent to massive particles moving in the resonator plane. If this system is operated in a regime in which reabsorption of cavity photons by the dye medium dominates over photon loss, a thermalization process of the photon gas to the temperature of the resonator at room temperature takes place. In earlier work, we have experimentally observed the thermalization process and, at sufficiently high photon densities, the Bose-Einstein condensation in the resonator ground mode [1], both under steady state conditions. The second order coherence of the condensate is found to be tuneable by adjusting the properties of the heat/particle reservoir created by the dye molecules (grandcanonical statistics) [2].
In recent experiments, we have studied the thermalization and condensation dynamics of the system with a streak camera after excitation with a short laser pulse. The timescale on which the photon gas becomes thermal (Bose-Einstein distribution) is found to be in the picosecond to nanosecond regime and is tuneable by various system parameters. In a second line of experiments, we create thermo-optically induced potentials for the two-dimensional photon gas by including a thermo-sensitive polymer to the resonator. This allows us to generate lattices of up to a few hundred photon condensates. Potential applications of this new microstructuring technique are studies of Mott-isolator physics, quantum Hall physics, and two-dimensional magnetism. Also, applications in optical computing seem conceivable.
[1] J. Klaers, J. Schmitt, F. Vewinger, and M. Weitz, Nature 468, 545 (2010)
[2] J. Schmitt, T. Damm, D. Dung, F. Vewinger, J. Klaers, and M. Weitz, Phys. Rev. Lett. 112, 030401 (2014)