Intense terahertz radiation from μm-gap GaAs photoconductive antenna

The terahertz pulse energy from photoconductive antenna is mainly derived from that stored in the static bias field. To obtain high intense THz radiation, the distribution of electrical field in semi-insulating GaAs photoconductive antennas was studied at square DC bias voltage. Due to the trap-enhanced space-charge, the electrical field is enhanced at anode and extent to cathode. So the highest effective terahertz radiation is obtained when the laser beam just overlaps the gap. A larger laser beam can reduce the Coulomb screening and radiation screening caused by a focused smaller beam, so the larger beam can increase the efficiency of antenna. At the same electrical field and laser power, an antenna with a larger gap can generate more intensive terahertz radiation than that with a smaller gap.