Fig. 2: Internal DFWM conversion efficiency for different samples, both on and off resonance.
From: Highly efficient THz four-wave mixing in doped silicon
The different doping densities (nD) and samples are given in the legend. Each curve is labelled by either the laser photon energy (\(\hbar\)ω in meV) or the resonant transition being excited. The ratio between pump pulse energies x = E2/E1 was kept constant in each case: values of x are given on each data set. The data are very close to cubic (\({E}_{3}={x}^{2}{E}_{1}^{3}/{E}_{{\rm{c}}}^{2}\) as expected), and the solid lines are fits to the low intensity portion. The fitted values of Ec are also indicated. For the high density Si:P sample, only one intensity was measured at each laser frequency and a cubic dependence (dashed lines) is shown for comparison with the other measurements
