Propagation of focused terahertz pulses through subcentimeter conductive apertures

Temporal waveforms of focused terahertz (THz) pulses, generated from a large-aperture photoconductive antenna, which were passed through conductive apertures were studied. The observed terahertz waveforms formed a large negative tail following the main peak, which was dependent on the aperture size. The observed features were reproduced by simulation using an analytic waveguide model which assumes a single cutoff frequency for the conductive aperture. This feature was observed using conductive apertures of subcentimeter (about 1 to 9mm) diameter and thickness. Distortion of THz waveforms can be caused when using typical optics such as metal crystal holders that are unintentionally put in the path of THz propagation. Approximately half-cycle pulses without tails were generated by carefully avoiding this effect.