  Near-field imaging with terahertz (THz) waves is emerging as a powerful
technique for fundamental research in photonics and across physical and life
sciences. Spatial resolution beyond the diffraction limit can be achieved by
collecting THz waves from an object through a small aperture placed in the
near-field. However, light transmission through a sub-wavelength size aperture
is fundamentally limited by the wave nature of light. Here, we conceive a novel
architecture that exploits inherently strong evanescent THz field arising
within the aperture to mitigate the problem of vanishing transmission. The
sub-wavelength aperture is originally coupled to asymmetric electrodes, which
activate the thermo-electric THz detection mechanism in a transistor channel
made of flakes of black-phosphorus or InAs nanowires. The proposed novel THz
near-field probes enable room-temperature sub-wavelength resolution coherent
imaging with a 3.4 THz quantum cascade laser, paving the way to compact and
versatile THz imaging systems and promising to bridge the gap in spatial
resolution from the nanoscale to the diffraction limit.
