Terahertz Near-Field Imaging of Biological Samples With Horn Antenna-Excited Probes

Abstract

We report terahertz near-field imaging of different biological samples with metallic, Teflon, and quartz (dielectric) probes excited with a horn antenna and using a terahertz vector network analyzer. The terahertz decay length ( $L_{d}$ ) of the metallic probe was $445~\mu \text{m}$ at 0.8375 THz ( $\lambda _{\mathrm {{free}}}\sim ~375~\mu \text{m}$ ), while the Teflon probe had $L_{\mathrm {{d}}}$ of $230~\mu \text{m}$ at 1.0422 THz ( $\lambda _{\mathrm {{free}}}\sim ~288~\mu \text{m}$ ), and the quartz probe had $L_{\mathrm {{d}}}$ of $75~\mu \text{m}$ at 0.8024–0.8424 THz ( $\lambda _{\mathrm {{free}}}\sim 288\mu \text{m}$ ). With these probes, we imaged a slice of mouse brain, a dwarf umbrella tree leaflet section, and a boxelder bug wing section. In the terahertz image of the mouse brain slice, we observed the outline of the different regions of the brain slice. In the terahertz image of the leaflet, the venation in the leaflet (because of its relatively high water content) was clearly observed at terahertz which was not well defined in its optical image. In the terahertz image of the bug wing section, the transition from the thick corium region to the thin membrane region had a profile that was different from its optical image. Finally, we demonstrated the capability of the near-field imaging system for imaging through a dielectric slab with internal structure that was clearly detected at terahertz, while it was completely concealed optically.