Pump-probe denegerate scattering of polaritons in a multiple microcavity.

Communication oraleMicrocavity polaritons are mixed states of confined photons and quantum well excitons. They inherit interesting properties from each of their two strongly-coupled components. Their excitonic part brings Coulomb interaction, and the photonic part brings cavity amplification and steep dispersion. Polaritons are particularly subject to parametric processes or four-wave mixing. Parametric amplification and oscillation have been observed in 2D single microcavities [1], in a “magic-angle" configuration. Engineering the geometry of the cavities allows overcoming the limitations of the process configuration in these microcavities, governed by conservation of energy and impulsion. Over the last years, disks, rings, wires [2] or pillars have been studied in addition to conventional 2D single microcavities. Multiple planar microcavities are another variant that allows new configurations to be studied. Several cavities can be stacked on top of each other, and coupled by their Bragg intermediate mirrors. Appropriate coupling results in several delocalized modes, where interbranch parametric processes can occur. The set of fourwave mixing configurations that conserve both energy and wave-vectors is consequently much richer. For example, parametric amplification and oscillation have been observed in a triple cavity in an angle-degenerate configuration [3,4]. Here we study parametric interaction in an energy-degenerate configuration. This situation is interesting because individual beams are spatially separated and can eventually be individually analyzed for other properties, such as noise and correlations, which are expected to show non-classical effects. In the present work, we concentrate on power dependences and polarization properties in a triple AlGaAs microcavity embedding InGaAs QWs. First, we demonstrate optical parametric amplification using a pump-probe geometry and cw Ti:Sa excitation (at 4K). Second, we study the idler polarization when varying the pump-probe relative polarization. The efficiency of the parametric amplification depends on the relative polarization of the pump, probe and idler beams in a way that is intrinsically related to the ratio of the coupling constants that characterize the polariton-polariton interaction strenght, for polaritons with parallel or antiparallel spins [5]. Here, we demonstrate that the ratio of these coupling constants can be determined in a very straightforward experiment. References [1] P. G. Savvidis et al., Phy. Rev. Lett. 84, 1547 (2000); M. Saba et al., Nature 414, 731 (2001). [2] G. Dasbach et al., Phys. Rev. B 71, 161308 (2005). [3] C. Diederichs and J. Tignon, Appl. Phys. Lett. 87, 251107 (2005). [4] C. Diederichs et al., Nature 440, 904 (2006) ; D. Taj et al., Phys. Rev. B 80, 081308 (2009). [5] I.A. Shelykh et al., Semicond. Sci. Technol. 25, 013001 (2010)