100 μm Resolution Terahertz Imaging via Inverse Spherical Synthetic Aperture Radar Imaging by Terahertz Time-Domain Spectroscopy

Abstract

Terahertz (THz) synthetic aperture imaging enables high-resolution imaging beyond the geometric and optical constraints of conventional focused THz setups. While traditional raster-scanning methods require planar objects and precise alignment, synthetic aperture techniques synthesize a large effective aperture from spatially distributed measurements, allowing flexible imaging of complex-shaped objects. In this work, an inverse spherical synthetic aperture is investigated. The setup employs a 3D printed motorized stage for azimuth and elevation scanning in combination with a THz time-domain spectroscopy (THz-TDS) system. Theoretical analysis are performed by modeling the pulse shape by a double Gaussian function to simulate the imaging response for the spherical aperture, with the circular aperture model revisited as a preliminary theoretical foundation. Key imaging parameters such as spatial resolution and peak sidelobe ratio (PSLR) are evaluated as functions of the aperture sampling. Experimental results demonstrate a spatial resolution of $55 \,\mathrm{\mu }\mathrm{m}$ for the circular aperture and 110$\mathrm{\mu }$$\mathrm{m}$ for the spherical aperture obtained with a bandwidth of around $2.7 \,\mathrm{T}\mathrm{Hz}$, centered at $1.4 \,\mathrm{T}\mathrm{Hz}$, confirming the potential of fine resolution imaging of complex-shaped objects by the synthetic aperture approach.