Terahertz microscope with oblique subwavelength illumination: design principle

Abstract

It is shown that the image contrast in the air when using a microscope based on dielectric microparticles with a size of the order of wavelength can be significantly enhanced with the help microparticles that provide the formation of the radiation localisation region at an angle to the direction of radiation incidence (at an angle to the optical axis). For this purpose, a screen is placed in front of the particle, which blocks part of the incident beam, forming a photonic hook or a photonic jet (terajet) with oblique illumination in the near field.

BaTiO3 microsphere assisted imaging of erythrocytes by light structuring photonic hook

“…In this case, it is possible to increase the optical image quality [27] by enhancing its contrast. The concept of a mesoscale particle-based microscope combining two approaches: the use of a) oblique illumination of an object b) utilizing structured subwavelength near field in the form of a photonic hook (PH), discovered in 2015 by Minins, was offered in [19]. A comparison of image quality between the photonic jet and the photonic hook was discussed in [19].…”

“…The concept of a mesoscale particle-based microscope combining two approaches: the use of a) oblique illumination of an object b) utilizing structured subwavelength near field in the form of a photonic hook (PH), discovered in 2015 by Minins, was offered in [19]. A comparison of image quality between the photonic jet and the photonic hook was discussed in [19]. It has been shown that a microscope with oblique illumination in the near field, which allows one, without using an immersion medium, to obtain images with ultra-high resolution inherent in photonic jets and high contrast.…”

“…This effect includes the socalled photonic jet effect [15]. Since then, optical [16,17] and terahertz [18,19] microscopes using dielectric wavelength-scaled particles began to develop rapidly. A resolution in lateral directions of λ/15 for objects of plasmonic metal [20] and λ/8 for dielectric objects [21] were experimentally achieved.…”

Terajet-assisted time-domain super-resolution imaging

“…Since then, objects of various three-dimensional shapes, such as cone, cuboid, disk, pyramid, etc have been proposed for nanojet generation [17][18][19]. A large number of works focuses on utilizing photonic nanojet for applications in microsphere-assisted optical [20,21] and THz microscopy [22], nondestructive real-time imaging beyond the diffraction limit [23], Raman spectroscopy [24], fluorescent sensing [25], nano-lithography [26], etc.…”

THz hooks generated on the basis of hollow reflection mirror

“…And the THz hook (TH) refers to the photonic hook generated in the THz frequency region, correspondingly. As a highly focused curved beam, the PH/TH has not only the aforementioned features of PNJ, but also the property of self-bending, which widens the application fields of the PNJ, such as trapping and manipulation of nanoparticles and cells [13,14], light switching [15,16], and imaging under oblique subwavelength illumination [17]. Furthermore, multiple PHs may find applications in batch manipulation of nanoparticles, control of multiple optical switches, and multi-channel reflective fluorescence/ confocal microscopy [18][19][20].…”