Polarization-sensitive THz solid immersion microscopy

Abstract

Terahertz (THz) technology has numerous applications in medical diagnostics and therapy, primarily relying on effective medium theory, which assumes biological tissues are optically isotropic and homogeneous at THz wavelengths. However, recent studies have revealed that mesoscale (~λ) heterogeneities within tissues can be visualized using THz microscopy. This creates a need to explore the scattering and polarization effects of THz radiation interacting with biological tissues, as appropriate tools have been lacking. To address this, we developed a polarization-sensitive THz microscope based on the solid immersion effect, operating in reflection mode. The system comprises a silicon hemispherical immersion lens, a metal wire-grid polarizer and analyzer, a backward-wave oscillator generating continuous-wave radiation at 0.6 THz (λ=500 μm), and a Golay detector. This setup enables the examination of local polarization-dependent THz responses in mesoscale tissue structures, achieving a resolution of up to 0.15λ. Using this method, we captured THz images of test samples at two orthogonal polarization states, revealing THz birefringence (structural optical anisotropy). We investigated the structural anisotropy of THz responses in porous biomorphic silicon carbide ceramics and obtained refractive index distributions for freshly excised rat brain tissue. Notably, significant THz birefringence was observed in the corpus callosum, which contains densely packed axons linking the cerebral hemispheres. These results underscore the potential of THz polarization-sensitive microscopy in biophotonics and medical imaging.

Speaker

Demyan D. Rybnikov
Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia
Russia

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