Abstract: Large-aperture biased photoconductive emitters which can generate high-power narrow-band terahertz (THz) radiation are developed. These emitters avoid saturation at high fluence excitation and achieve enhanced peak power spectral density by employing a thick layer of short lifetime low- temperature-grown GaAs (LT-GaAs) photoconductor and multiple-pulse excitation. THz waveforms are calculated from the saturation theory of large-aperture photoconductors, and a comparison is made between the theory and the measurement. A direct comparison of the multiple-phase saturation properties of terahertz emission from semi-insulating GaAs and LT-GaAs emitters with different carrier lifetimes reveals a strong dependence of the multiple pulse saturation properties of terahertz emission on the carrier lifetime. In particular, the data demonstrate that saturation is avoided only when the interpulse spacing is longer than the carrier lifetime.!23
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