The authors describe the saturation properties of ultrafast pulsed electromagnetic radiation generated by large-aperture photoconducting antennas as a function of optical excitation fluence. A theory that predicts this effect is presented. The amplitude saturation of the radiation has been observed form antennas incorporating GaAs, InP, and radiation damaged silicon-on-sapphire consistent with theoretical expectations. The radiated fields were measured directly with a time resolution of 0.6 ps with the use of a large-aperture antennas as a detector. From these experimental studies, information about the high-speed response (i.e., the transient carrier mobility in the first few picoseconds after optical excitation) of the photoconductors incorporated in the antenna can be obtained under conditions of high applied electric fields and optical fluences.
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