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5Super-resolution THz microscopy and endoscopy of biological tissues
N.V. Chernomyrdin1*, V.A. Zhelnov1, D.R. Il'enkova1, D.D. Rybnikov1, A.A. Gavdush1, A.S. Kucheryavenko2, G.M. Katyba2, V.N. Kurlov2, I.E. Spektor1, K.I. Zaytsev1
1-Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia
2- Institute of Solid State Physics of the Russian Academy of Sciences, Chernogolovka, Russia
Terahertz (THz) technologies are finding numerous applications in biophotonics and medical diagnosis [1-3]. However, some problems are still inherent to THz optical systems, among them: low spatial resolution [4] and lack of efficient endoscopes [5]. In our work we develop methods of superresolution THz microscopy based on solid immersion (SI) effect. This approach allows to overcome Abbe diffraction limit by focusing electromagnetic beam at a small distance behind SI lens made of high-index material [4]. SI optical system can reach resolution up to 0.15X (where X is a free-space wavelength) using high-resistivity silicon SI lens [6,7], and even up to 0.06X using rutile SI lens [9]. Developed THz SI microscope was applied for studying dielectric media and different types of healthy and pathological biological tissues ex vivo [6,7,9]. THz SI microscope coupled with linear polarizer and analyzer was applied to study optical anisotropy of rat brain tissues ex vivo [10]. In our works we also introduce THz waveguides and endoscopes based on sapphire shaped crystals, which provide low dispersion and low radiation loss [5,11]. Sapphire waveguides based on photonic crystal or antiresonant mechanisms of radiation transfer were manufactured using edge-defined film-fed growth (EFG) technique without any polishing or drilling [12]. We have developed THz endoscope based on antiresonant hollow-core sapphire waveguide coupled with a sapphire SI lens and experimentally demonstrated 0.2X focal spot diameter of this endoscope [13]. We have also proposed an approach for THz refractometry of hard to access objects based on a hollow-core antiresonant waveguide, formed by a polytetrafloroethylene (PTFE)-coated sapphire tube with the outer end closed by a monolithic sapphire window [14].
[1] O.A. Smolyanskaya, et al, Terahertz biophotonics as a tool for studies of dielectric and spectral properties of biological tissues and liquids, Progress in Quantum Electronics, Vol. 62, P. 1-77 (2018).
[2] K.I. Zaytsev, et al, The progress and perspectives of terahertz technology for diagnosis of neoplasms: a review, Journal of Optics, Vol. 22, P. 013001 (2020).
[3] N.V. Chernomyrdin, et al, Terahertz technology in intraoperative neurodiagnostics: A review, Opto-Electronic Advances, Vol. 6, № 4. P. 220071 (2023).
[4] N.V. Chernomyrdin, et al, Terahertz solid immersion microscopy: Recent achievements and challenges, Applied Physics Letters, Vol. 120, № 11, P. 110501 (2022).
[5] G.M. Katyba, et al, Sapphire waveguides and fibers for terahertz applications, Progress in Crystal Growth and Characterization of Materials, Vol. 67, № 3, P. 100523 (2021).
[6] N.V. Chernomyrdin, et al, Reflection-mode continuous-wave 0.15X-resolution terahertz solid immersion microscopy of soft biological tissues, Applied Physics Letters, Vol. 113, № 11, P. 111102 (2018).
[7] N.V. Chernomyrdin, et al, Quantitative super-resolution solid immersion microscopy via refractive index profile reconstruction, Optica, Vol. 8, № 11, P. 1471-1480 (2021).
[8] V.A. Zhelnov, et al, Hemispherical Rutile Solid Immersion Lens for Terahertz Microscopy with Superior 0.06-0.11X Resolution, Advanced Optical Materials, Vol. 12, № 1, P. 2300927 (2024).
[9] A.S. Kucheryavenko, et al, Terahertz dielectric spectroscopy and solid immersion microscopy of ex vivo glioma model 101.8: brain tissue heterogeneity, Biomedical Optics Express, Vol. 12, № 8, P. 5272-5289 (2021).
[10] N.V. Chernomyrdin, et al, Quantitative polarization-sensitive super-resolution solid immersion microscopy reveals biological tissues' birefringence in the terahertz range, Scientific Reports, Vol. 13, № 1, P. 16596 (2023).
[11] K.I. Zaytsev, et al, Terahertz photonic crystal waveguides based on sapphire shaped crystals, IEEE Transactions on Terahertz Science and Technology, Vol. 6, № 4, P. 576-582 (2016).
[12] G.M. Katyba, et al, Sapphire shaped crystals for waveguiding, sensing and exposure applications, Progress in Crystal Growth and Characterization of Materials, Vol. 64, № 4, P. 133-151 (2018).
[13] A.S. Kucheryavenko, et al, Super-resolution THz endoscope based on a hollow-core sapphire waveguide and a solid immersion lens, Optics Express, Vol. 31, № 8, P. 13366 (2023).
[14] G.M. Katyba, et al, Terahertz refractometry of hard-to-access objects using the sapphire endoscope suitable for harsh environments, Applied Physics Letters, (Accepted in 2024).
