Terajet-assisted time-domain super-resolution imaging

Large-scale applications of real-time terahertz (THz) imaging are often limited by the spatial resolution of a THz microscope. One of the simplest approaches to circumvent this problem in practice and achieve resolution below the diffraction limit consists in placing a dielectric particle with a size comparable to the radiation wavelength in the vicinity of the focal plane of the THz imaging system. Here, we theoretically consider the transmittance of a THz Gaussian beam through a Teflon sphere to further analyze experimental results on THz superresolution imaging. We address the resolution beyond the diffraction limit (the experimentally determined value is 0.38 lambda at 0.46 THz) through the superlens effect of the terajet generated by the mesoscale sphere owing to propagating and evanescent partial waves in the terajet. Due to the coupling of the dielectric sphere and time-domain THz spectrometer, we can detect a 10 mu m thick PTFE film, which is almost transparent (98% transmittance) in the THz frequency range. The correlation between the transmittance spectrum of the dielectric sphere and the quality of THz images of thin, nonconducting films collected at different frequencies has been demonstrated experimentally and considered analytically. Our study is relevant for hyperspectral imaging applications and further development of the sphere-coupled time-domain THz imaging technique.