Beam characteristics in a terahertz broadband sub-wavelength imaging system using a solid immersion lens

This research explores the spatial and spectral beam characteristics in a terahertz (THz) broadband sub-wavelength imaging system employing a solid immersion lens. Previously, we demonstrated a broad-spectrum sub-wavelength THz imaging setup by integrating a SIL with a THz time-domain spectrometer (TDS). The primary focus of the current study lies in analyzing key parameters that influence beam characteristics and subsequently affect the performance of the imaging system, including SIL misalignment tolerances and beam propagation from the SIL. Numerical simulations demonstrate that the system can withstand millimeter-level transverse and longitudinal displacements in the SIL position. Furthermore, numerical simulations of beam propagation characteristics indicate that the system achieves sub-wavelength imaging resolution up to 1 mm from the SIL at 0.5 THz, thus highlighting its potential for non-destructive testing of subsurface structures. These findings are validated experimentally through imaging stacked utility knife blades bearing sub-wavelength structures across the frequency range of 0.2 to 2 THz.