A method for characterizing terahertz radiation using spectral domain interferometry, comprising overlapping a pump beam and a terahertz beam in a detecting crystal; obtaining two probe pulses by propagating the probe beam into a polarization maintaining single-mode optical fiber after the detecting crystal; and measuring a change in the optical path difference between the two probe pulses. The system comprises a detection crystal, where a terahertz pulse and a probe beam are made to overlap; a polarization-maintaining optical fiber propagating the probe beam after the detection crystal and outputting two probe pulses; and a spectrometer where the two probe pulses interfere.