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Optics and Spectroscopy, 2023 Volume 131, Issue 6, Pages 880–887 (Mi os1390)

Proceedings of The XXVI Annual International Conference "Saratov Fall Meeting 2022", September 26-30, 2022, Saratov, Russia
Biophotonics

Combination of hollow-core sapphire waveguide and immersion lens for ultra-high resolution THz endoscopy

A. S. Kucheryavenkoa, V. A. Zhelnova, N. V. Chernomyrdinb, V. N. Kurlova, K. I. Zaitsevb, G. M. Katybaa

a Osipyan Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Russia
b Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia

Abstract: The development of terahertz (THz) imaging methods is hampered by the low spatial resolution of traditional diffraction-limited imaging systems, mainly due to the large wavelength of used radiation (from a few of mm to tens of $\mu$m). To solve this problem, we have proposed a new method of THz endoscopy with subwavelength spatial resolution, which is designed to study hard-to-reach areas of living organisms in vivo. A hollow-core sapphire tube with polytetrafluoroethylene outer coating is used as a waveguide, in which the antiresonant principle of radiation transmission is implemented. The waveguide and the immersion lens are optimized to provide high optical characteristics in a given wavelength range to ensure the best focusing. Two immersion lenses made of sapphire and silicon were developed and fabricated, which were then mounted on plane-parallel windows fixed on the rear end of the waveguide. The study of the field intensity distribution on the shadow side of the glqq “waveguide–lens”system revealed a focal spot diameter of $\simeq$0.2$\lambda$ in the case of a lens made of sapphire and $\simeq$0.3$\lambda$ in the case of a lens made of crystal silicon at a wavelength $\lambda$ = 500 $\lambda$m, which significantly exceeds the Abbe diffraction limit. This agrees with our numerical predictions and demonstrates the promise of using the proposed endoscope for measurements with subwavelength resolution.

Keywords: terahertz radiation, terahertz imaging, endoscopy, subwavelength spatial resolution, Abbe diffraction limit, solid immersion effect.

Received: 07.02.2023
Revised: 13.02.2023
Accepted: 16.02.2023

DOI: 10.21883/OS.2023.06.55925.123-23



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