Low-frequency spectral enhancement of THz electromagnetic waves emitted from InAs surface with increased excitation intensity

We studied the excitation intensity dependence of the spectrum of the THz electromagnetic waves emitted from the surface of InAs excited by a femtosecond laser pulse. An enhancement of the spectral amplitude in the low-frequency regime (<0.6 THz) of the THz electromagnetic waves was observed when the excitation intensity was increased. To clarify the mechanism of the above phenomenon, we also performed THz wave emission experiments using a semi-insulating-GaAs sample. Due to the difference of the band-gap energies between InAs and GaAs, carriers excited to the conduction band experience different relaxation processes when they are excited by a laser pulse with a photon energy of 1.5 eV. Comparison of the experimental results for InAs and GaAs showed that the suppression of the intra-band relaxation induces the enhancement of the amplitude of the THz spectrum in the low-frequency regime for InAs. (C) 2004 American Institute of Physics.