Near-Field Imaging and Spectroscopy with Terahertz Radiation
April 25th, 2019 TOM SIDAY University College London

Terahertz (THz) radiation (~0.3 – 10 THz) interacts in unique ways with materials and devices, and using THz near-field microscopy, these interactions can be imaged with extreme subwavelength resolution. However, traditionally, THz near-field microscopes have lacked sensitivity. In this talk, I will discuss how we have improved the sensitivity of THz near-field microscopes through the development of two near-field techniques: scattering-type near-field microscopy (s SNOM), and collection-mode aperture probes. These improvements could make imaging phenomena with low THz contrast, such as polaritons in 2 dimensional materials, or biological systems far more practical.

Scattering-type near-field microscopy (s-SNOM) can achieve spatial resolution as high as 5 nm. However, the signal to noise ratio (SNR) of this technique is intrinsically low due to inefficient scattering of the near-field interaction at the probe apex into the far-field where it can be detected. By designing the scattering probe to act as a resonant dipole antenna, the efficiency of this process can be significantly improved.

Collection-mode aperture probes have limited spatial resolution due to the Bethe dependence: The small aperture allows for practically zero THz transmission. This limitation can be overcome by designing efficient detectors using both plasmonic and dielectric metasurfaces, and integrating these with the aperture probe into a single device.

Seminar, April 25, 2019, 13:30. ICFO’s Seminar Room

Hosted by Prof. Frank Koppens