Pulsed THz solid immersion microscopy with subwavelength resolution

In this work we developed reflection-mode terahertz (THz) pulsed solid immersion microscope based on a wide-aperture silicon solid immersion lens and two photoconductive antennas (PCA) operating in tandem as a source and detector of broadband THz pulses. Such configuration combines the superresolution of a THz solid immersion optical system and a large amount of information provided by the THz pulsed spectroscopy approach. THz pulsed microscope forms a three-dimensional data array by raster scanning of the sample. This data can be represented in the time and frequency domains which paves the way for THz signal processing. The spatial resolution of our microscope depends on the form of THz image representation. The resolution ranges from 0.136$\lambda_с$ to 0.2$\lambda_с$ when THz image is formed in time domain. While for the case of spectral domain image representation in frequency range 0.5–1.7 THz, the resolution is 0.147$\lambda$–0.304$\lambda$ and 0.047$\lambda$–0.156$\lambda$ for the amplitude and phase detection modes, respectively. The highest resolution obtained in the phase domain results from the nonlinearity of this method of image construction. Obtained results demonstrate the potential of the THz pulsed solid immersion microscope to visualize subwavelength elements of objects with simultaneous registration of spectral data, which makes it applicable in biophotonics, condensed matter physics, nondestructive testing and other fields.