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8The 30th International Conference on Advanced Laser Technologies N-I-16
ALT'23
Super-resolution THz imaging of biological tissues: Recent achievements and challenges
Kirill I. Zaytsev
Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia
E-mail: kirzay@smail.com
Unique effects of THz-wave-matter interaction push rapid progress in THz optoelectronics aimed at bridging the problematic THz gap [1]. However, majority of the THz technology applications still suffers from low spatial resolution of common lens- or mirror-based THz optics [2]. In fact, such optics cannot overcome the ~0.5X Abbe limit and provides the resolution larger than a free-space wavelength X (i.e., a few hundreds of micrometers or even a few millimeteres) [3,4]. This humpers the use of THz technology in vigorously-explored biomedical applications [5]: diagnosis of malignant and benign neoplasms [6-8], diabetes mellitus [9,10], cancer therapy [11], etc.
To mitigate this difficulty, supper-resolution THz imaging modalities were recently introduced. Among them, we particularly underline different methods of the THz scanning-probe near-field optical microscopy. They rely on strong light confinement on sub-wavelength probes and provide the advanced resolution as high as ~10-1-10-3A, [12]. Meanwhile, they suffer from small energy efficiency (or presume an interplay between resolution, energy efficiency, field of view, and operation rate), while the scanning probe may interact with an imaged sample an even perturb its structure.
In our research, we developed a novel super-resolution THz imaging modality - so-called, THz solid immersion (SI) microscopy [2,13-22]. The essence of a SI effect is a reduction in the electromagnetic beam caustic dimensions, when it is formed in free space, at small distance behind the high-refractive-index materials. We developed the THz SI lens, that is based on a wide-aperture aspherical singlet [3] and a near-focal composite silicon hemisphere, operates in reflection mode, and provides the resolution as high as 0.15A, (beyond the Abbe limit) [14]. It possesses advanced energy efficiency thanks to the absence of any near-field probes in an optical scheme, as well as adapted for imaging of soft biological tissues, thanks to the composite construction of the hemisphere [14]. We also studied capabilities of a bulk sapphire crystal [21], a bulk rutile crystal (with its impressive THz refractive index of ~10) [22], and a compound of rutile microparticles and polymer [17], as favourable material platforms of the THz SI optics.
All these modalities of super-resolution THz imaging were recently applied in biophotonics, where they allow for the highly-accurate delineation of the tumor margins, studying the tissue heterogeneity at the THz wavelengths scale and the related scattering effects [18-20]. In this talk, we discuss, recent achievements and challenging problems in super-resolution THz imaging of tissues.
This work was supported by the Russian Science Foundation, Project # 22-79-10099.
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[22] V.A. Zhelnov et al., "Hemispherical rutile solid immersion lens for rerahertz microscopy with superior 0.06-0.1R resolution," Advanced Optical Materials (2023), under review.
