Generation and characterization of terahertz pulse trains from biased, large-aperture photoconductors

The saturation properties of terahertz emission from biased, large-aperture photoconductors excited by trains of amplified femtosecond optical pulses are presented. A direct comparison is made of the multiple-pulse saturation properties of terahertz emission from semi-insulating GaAs and low-tempera ture-grown GaAs emitters with different carrier lifetimes. When the carrier lifetime is less than or comparable with the interpulse spacing, a signifi cant enhancement of the narrow-band terahertz output is observed. The enhan cement is not observed for emitters with long carrier lifetimes, consistent with the results of a previously derived saturation theory [Opt. Lett. 18, 1340 (1993)]. (C) 1999 Optical Society of America. OCIS codes: 320.7160, 3 20.7080, 320.7100, 320.7130.