  Recently, computational sampling methods have been implemented to spatially
characterize terahertz (THz) fields. Previous methods usually rely on either
specialized THz devices such as THz spatial light modulators, or complicated
systems requiring assistance from photon-excited free-carriers with high-speed
synchronization among multiple optical beams. Here, by spatially encoding an
800 nm near-infrared (NIR) probe beam through the use of an optical SLM, we
demonstrate a simple sampling approach that can probe THz fields with a
single-pixel camera. This design does not require any dedicated THz devices,
semiconductors or nanofilms to modulate THz fields. Through the use of
computational algorithms, we successfully measure 128$\times$128 field
distributions with a 62 $\mu m$ transverse spatial resolution, more than 15
times smaller than the central wavelength of the THz signal (940 $\mu m$).
Benefitting from the non-invasive nature of THz radiation and sub-wavelength
resolution of our system, this simple approach can be used in applications such
as biomedical sensing, inspection of flaws. in industrial products, and so on.
