Super-resolution THz endoscope based on a hollow-core sapphire waveguide and a solid immersion lens

To address a challenging problem of super-resolution terahertz (THz) endoscopy, in this paper, an antiresonant hollow-core waveguide was coupled with a sapphire solid immersion lens (SIL), aimed at subwavelength confinement of guided mode. The waveguide is formed by a polytetrafluoroethylene (PTFE)-coated sapphire tube, the geometry of which was optimized to ensure high optical performance. SIL was judiciously designed, fabricated of bulk sapphire crystal, and then mounted at the output waveguide end. Study of the field intensity distributions at the shadow side of the waveguide-SIL system revealed the focal spot diameter of similar or equal to 0.2 lambda at the wavelength of lambda= 500 mu m. It agrees with numerical predictions, overcomes the Abbe diffraction limit, and justifies super-resolution capabilities of our endoscope.(c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

To tackle the challenge of super-resolution terahertz endoscopy, this paper proposes the use of an antiresonant hollow-core waveguide coupled with a sapphire solid immersion lens (SIL) for subwavelength confinement of guided mode. The optimized geometry of the PTFE-coated sapphire tube waveguide ensures high optical performance, while the judicious design and fabrication of the bulk sapphire crystal SIL, mounted at the output end of the waveguide, allows for a focal spot diameter of approximately 0.2 lambda at a wavelength of lambda = 500 mu m. This confirms the super-resolution capabilities of the proposed endoscope, surpassing the Abbe diffraction limit.