text: Previously called "ideal ATM" and "polarization-varying ATM," stationary sample ATM (SSATM) involves rotation of the linearly polarized state of the THz beam in a time-domain spectroscopy (TDS) configuration parallel to the interrogated material sample. In a SSATM configuration, the THz beam polarization is rotated through 360° in a plane perpendicular to the propagation direction of the beam. Measurements of the sample's anisotropy is measured at several THz polarization angles.
  At least two methods to achieve THz polarization rotation for SSATM have been demonstrated: 1) by using a THz quarter waveplate (THz-QWP) together with an infrared polarizer  and 2) by rotating the photoconductive antenna.
  In the case of employing a THz-QWP and an infrared polarizer, the magnitude of the measured signal, , where  is a time delay between THz generation and the detected pulses in a THz-TDS system is dependent on the relative polarization angle of the THz light,  and the polarization angle of the ultrafast near-infrared (NIR) probe beam, , at the sample by the relationship
  The objective is to maintain equal magnitude of the THz electric field at the sample for all measurement angles, . This requires adjustment of  for every .