Abstract

The dynamics of cavity polaritons in microcavities is presently debated, in particular whether or not the so-called Boser action is responsible for the observed laser-like emission from polaritons with zero in-plane wave vector (k_‖ ~ 0), shown in the far-field image in the inset of Fig. (a).[1,2] This action relies on the bosonic nature of low-density polaritons enhancing scattering processes stimulated by the final-state polariton population n_LP. A particular issue is if this should be distinguished from a parametric process, that has provided large pulse amplification under angle-resonant pumping conditions for polariton-polariton scattering on the lower-polariton branch.[3] In this work we time resolve the k_‖ ~ 0 self-stimulated emission under similar excitation conditions (with a single pulse - see inset in Fig. (b)) in microcavities (MC) with differently broadened single quantum wells (QW). One sample (HMC in (b)) is homogeneously broadened with bare QW linewidth δ = 120 μeV < δ_MC = 260 μeV (the bare MC linewidth) and one sample (IMC in (a)) is inhomogeneously broadened with δ = 1.0 meV ≫δ_MC.[4] In contrast to the HMC, the self-stimulated emission transient in the IMC is much slower and the emission maximum does not shift to earlier times with increasing excitation density, if coherences should play a dominant role in the dynamical response, it should result in faster dynamics for increasing inhomogeneous broadening T, because of the well-known shortening of the dephasing time ${\left(T_2^{*}\right)}^{-1}=T_2^{-1}+\Gamma$. We therefore conclude that there is a dominant contribution to the low-density polariton dynamics in microcavities from population effects under angle-resonant excitation conditions, which is in agreement with a rate-equation model with the bosonic enhancement factor (1+n_LP) (not shown). [5] However, the strong emission is caused by the fast build-up of a coherent k_‖ ~ 0 polariton population resulting in the emitting polarization. Thus, the emission process is like in a parametric process with n_LP≫1 and therefore indistinguishable from the final-state stimulated polariton dynamics.

© 2000 IEEE