Nonlinear spectroscopy of exciton-polaritons in a GaAs-based microcavity

TL;DR

This study investigates two-photon excitation in a GaAs microcavity, revealing second harmonic generation linked to polariton states and exploring exciton states relevant for terahertz lasing, with findings on the efficiency of two-photon pumping.

Contribution

It provides a systematic analysis of nonlinear two-photon processes in exciton-polariton microcavities, highlighting the dependence on polariton composition and the challenges in detecting certain exciton states.

Findings

Second harmonic generation depends on the photonic fraction of polaritons.

No clear evidence of 2p exciton states was observed.

Two-photon pumping efficiency appears low.

Abstract

We present a systematic investigation of two-photon excitation processes in a GaAs-based microcavity in the strong-coupling regime. We observe second harmonic generation resonant to the upper and lower polariton level, which exhibits a strong dependence on the photonic fraction of the corresponding polariton. In addition we have performed two-photon excitation spectroscopy to identify $2p$ exciton states which are crucial for the operation as a terahertz lasing device, which was suggested recently [A. V. Kavokin et al., Phys. Rev. Lett. \textbf{108}, 197401 (2012)]. However, no distinct signatures of a $2p$ exciton state could be identified, which indicates a low two-photon pumping efficiency.