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Time- and angular-resolved terahertz spectroscopy

Research in the terahertz regime of the electromagnetic spectrum has become increasingly prominent in photonics for a number of reasons, including the abilities to temporally resolve ultrashort pulses (~ ps), extract polarization information, and easily create structures with size on the order of the wavelength. In a conventional time-domain terahertz spectroscopy system, when a pulse of radiation is incident on a sample, the system detects the radiation transmitted along the incident beam axis. While this approach has proven to be effective for numerous applications, it is often desirable to detect radiation scattered from a sample at off-axis angles. The realization of a pump-probe terahertz spectroscopy system capable of time- and polarization-resolved detection at arbitrary angles is nontrivial, however, since the sampling probe pulse must retain its spatial alignment, polarization, and timing at all detection angles. In this work, we unveil a system capable of angular- and time-resolved detection of terahertz radiation, with detection angles spanning 360°. Moreover, the polarization of the radiation can be determined at any detection angle. The performance of the system is demonstrated experimentally by detecting the radiation scattered from a spherical sample, which exhibits a radiation pattern that is symmetric about the incident beam axis. To the best of our knowledge, an angularly resolved terahertz system with such versatility has not been previously realized, and its development introduces a new platform for explorations into angular dependent phenomena.