Transition from photocurrent surge to resonant optical rectification for terahertz generation in p-InAs

It has been demonstrated that the key to complete understanding of the mechanisms for terahertz (THz) generation from a p-type InAs wafer pumped by a subpicosecond Ti:sapphire amplifier lies in the dependences of the THz polarization on the azimuthal angle and polarization of the pump beam. At low enough pump intensities, photocurrent surge is the dominant mechanism for THz generation. However, the THz radiation originating from photocurrent surge is greatly reduced with increased pump intensity. Therefore, at sufficiently high pump intensities resonant optical rectification becomes the dominating mechanism for THz generation. The highest output power is measured to be 57 microW.