High-resolution polarization-sensitive solid immersion microscopy of biological tissues in the terahertz frequency range
Terahertz (THz) technology holds significant potential for label-free medical diagnosis and therapy, offering numerous applications. However, these applications often rely on the effective medium theory, assuming biological tissues to be optically isotropic and homogeneous at the scale of THz wavelengths. Recent research has revealed that tissues exhibit mesoscale (∼λ) heterogeneities, where λ represents the wavelength. This discovery has raised challenges in studying the scattering and polarization effects of THz-wave interactions with tissues, mainly due to the lack of suitable tools and instruments for such investigations. To address this challenge we have developed a polarization-sensitive reflection-mode THz solid immersion (SI) microscope. This microscope utilizes a silicon hemisphere-based SI lens, a metal-wire-grid polarizer and analyzer, a continuous-wave 0.6 THz backward-wave oscillator (BWO), and a Golay detector. The innovation of this microscope lies in its ability to study the local polarization-dependent response of mesoscale tissue elements with an impressive resolution of up to 0.15λ (where λ is the THz wavelength). We estimated developed microscope using metal objects featuring optical anisotropy in THz frequency range and applied it to study different types of biological tissues. Obtained results demonstrate the potential of polarization-sensitive THz microscopy in the fields of biophotonics and medical imaging, enabling more comprehensive studies of tissue structures and properties at the mesoscale level.
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Prokhorov General Physics Institute of the Russian Academy of Sciences