Generation and detection of terahertz radiation with large-aperture photoconducting antennas

Large-aperture photoconducting antennas produce and detect in a phase-sensitive manner optically steerable, directional, ultrashort pulsed electrical transients extending from d. c. to beyond 1 THz in frequency. The coherent nature of the detection technique gives rise to the obtainment of spectral information from a time domain waveform of the radiated electric field. A theory describing the behavior of these antennas excited by femtosecond optical pulses is presented.; Experiments performed to study the properties of these devices involve the use of a multikilohertz repetition rate stable train of femtosecond pulses amplified by a dye amplifier pumped by copper vapor laser pulses of a rectified polarization. A receiver based on a large-aperture design is optimized with respect to different photoconductors and dimensions both to be as sensitive and to have the best time resolution as possible. The measured spatial and temporal properties of this radiation are discussed with reference to the model describing it. Saturation of the radiated field generated from a large-aperture transmitter is predicted and observed from antennas incorporating GaAs, InP and radiation damaged silicon-on-sapphire. From the saturation experiments, 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 high optical fluences.; A large-aperture photoconducting transmitter is designed to produce terahertz radiation as efficiently as possible. The choice of photoconductor and gap spacing depend on the optical excitation pulse energy and the previously studied transient response of photoconductors used in large-aperture emitters. This large-aperture transmitter produces high-amplitude terahertz radiation that is detected with a high dynamic range of sensitivity. Such radiation can be used in the nonlinear spectroscopy of semiconductors, semiconductor devices and dielectrics and pulsed radar.