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.
@article{arxiv.1408.0917,
title = {Nonlinear spectroscopy of exciton-polaritons in a GaAs-based microcavity},
author = {Johannes Schmutzler and Marc Aßmann and Thomas Czerniuk and Martin Kamp and Christian Schneider and Sven Höfling and Manfred Bayer},
journal= {arXiv preprint arXiv:1408.0917},
year = {2014}
}