text: The original problem responsible for the "Terahertz gap" (the colloquial term for the lack of techniques in the THz frequency range) was that electronics routinely have limited operation at frequencies at and above 10 Hz. Two experimental parameters make such measurement possible in THz-TDS with LT-GaAs antennas: the femtosecond “gating” pulses and the < 1 ps lifetimes of the charge carriers in the antenna (effectively determining the antenna's “on” time). When all optical path lengths have fixed length, an effective dc current results at the detection electronics due to their low time resolution. Picosecond time resolution does not come from fast electronic or optical techniques, but from the ability to adjust optical path lengths on the micrometer (μm) scale. To measure a particular segment of a THz pulse, the optical path lengths are fixed and the (effective dc) current at the detector due to the a particular segment of electric field of the THz pulse.
  THz-TDS measurements are typically not single-shot measurements.