each other, and reasonable limiting conditions can be applied at high and low frequency, outside of the measured range. THz-TDS, in contrast, does not require use of Kramers-Kronig relations. By measuring the electric field of a THz pulse in the time-domain, the amplitude and phase of each frequency component of the THz pulse are known (in contrast to the single piece of information known by a power measurement). Thus the real and imaginary parts of an optical constant can be known at every frequency within the usable bandwidth of a THz pulse, without need of frequencies outside the usable bandwidth or Kramers-Kronig relations. See also Time resolved microwave conductivity References Further reading Spectroscopy Terahertz technology Explosive detection