Terahertz continuous-wave solid immersion imaging with spatial resolution beyond the Abbe limit

Abstract

We have proposed an approach to improve the resolution of terahertz (THz) imaging using the effect of solid immersion – i.e. a reduction in the dimensions of the electromagnetic beam caustic by its formation in a free space, behind the medium possessing high refractive index. We have designed a THz solid immersion lens (SIL) comprised of a polymer wide-aperture aspherical singlet and a crystalline truncated sphere mounted in front of the image plane. We have proposed an approach for the object handling at the focal plane of the THz SIL. We have combined numerical simulations and experimental studies to demonstrate the advanced 0.2λ spatial resolution of the proposed THz SIL – it is beyond the 0.5λ Abbe limit. Finally, we have assembled the continuous-wave THz SIL imaging system and applied it for studying various objects with sub-wavelength variations of structure and dielectric properties.