Interferometric four-wave-mixing spectroscopy on bulk GaAs

A phenomenon in interferometric four-wave mixing is reported which can be used to quantify effects beyond the third-order perturbational limit in a sensitive and intuitive fashion. The experiments on bulk GaAs at T=77 K on a time scale of 10 fs and at excited carrier densities as low as 2.3×{}10¹⁴{ncm}^{{{-}}3}$ show that the third- order perturbational limit can hardly be reached experimentally.