Scaling of terahertz radiation from large-aperture biased InP photoconductors.

We present a theoretical and experimental investigation into the generation of subpicosecond pulses of terahertz radiation from large-aperture biased photoconductors with 1.5-eV photon excitation. A model that describes the far-field radiation from the optically excited, biased photoconductor is developed. The peak of the radiated electric field as well as waveforms are presented as a function of optical excitation fluence and pulse width. The dependence of the terahertz radiation from biased InP and GaAs emitters on the applied bias field and on incident optical fluence for bias fields as high as 12 kV/cm and for optical fluences of 0.01–1.0 mJ/cm2 is presented. For a given level of optical excitation the radiated electric field is predicted by theory to scale linearly with the applied bias field. This prediction is verified experimentally, with radiated-field strengths as high as 1.23 ± 0.13 kV/cm being demonstrated. The radiated electric field also exhibits the monotonic saturation behavior predicted by theory, and saturation fluences of 0.058 ± 0.015 and 0.018 ± 0.008 mJ/cm2 are obtained for InP and GaAs emitters, respectively.

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