Comparison of THz (far-infrared) time domain spectroscopy and FTS methods

This paper will first describe the optoelectronic generation and detection of freely-propagating fsec pulses of THz electromagnetic radiation, and then applications of the THz beam system to THz time-domain spectroscopy (TDS) will be presented. Via optoelectronic excitation, a transient point source of THz radiation is generated at the focus of a dielectric collimating lens, followed by an additional paraboloidal focusing and collimating mirror. This source produces well collimated beams of fsec pulses of THz radiation. Matched to an identical receiver, the resulting system has extremely high collection efficiency (1). With a demonstrated signal-to-noise ratio of 1000, a time resolution of less than 150 fsec and a frequency range from 0.2 THz to more than 5 THz, (1 THz = 33.3 cm-1 = 4.1 meV), the performance of this optoelectronic THz system is limited by the intrinsic response time of the semiconductor (2).