High-intensity terahertz pulses at 1-kHz repetition rate

We report the generation of terahertz pulses with 0.4-/spl mu/J pulse energy at 1-kHz repetition rate using a large-aperture GaAs photoconductor with 3-cm gap aluminum electrodes, biased at voltages up to 45 kV. The terahertz output energy saturates at a laser fluence of 40 /spl mu/J/cm/sup 2/ at low-bias fields, while no clear saturation point was observed at high-bias fields. The output was found to be dependent on the repetition rate: at high fluences, pulse energy at 1 kHz is higher than that at 100 Hz by as much as 60%. A study of the behavior of the terahertz pulse energy and pulsewidth as a function of the pulsewidth of the laser excitation was conducted and compared with theoretical predictions. Propagation properties of the terahertz beam were also characterized, leading to a focal spot size as small as 800 /spl mu/m at the focus of a 2.5-in focal length parabolic mirror.