A new publication from Opto-Electronic Science; DOI 10.29026/oes.2022.210008 overviews how the cutoff of a spherical or cylindrical mesoscale particle can lead to a new optical resonant effect.
In this paper, a novel resonant phenomenon arising in the scattered near field of Janus particles, which allows the near field enhancement of local electric and magnetic fields, was demonstrated. A truncated sphere or cylinder was considered as a Janus dielectric wavelength-scaled (mesoscale) particle. It has been shown that the use of Janus particles can contribute to an increase in the figure of merit and an increase in the electric and magnetic field intensity components near the flat (cutting) surface of the distant element of the particle. The effect is resonant in relation to the volume of the removed fraction of the substance and was observed in the size range R: 5λ~15λ. It is shown that essentially subwavelength highly localized regions of the electric and magnetic fields appear near the flat surface of the particle. It is a new mechanism of the electromagnetic field deep subwavelength localization. Moreover, the truncated sphere or cylinder demonstrate support an elegant method for generating WGM when a particle is illuminated by a plane wavefront from the side of a curved (not cut off) surface.
The research groups of Profs. Igor V. Minin and Oleg V. Minin from Tomsk Polytechnic University, Dr. Zengbo Wang from the Bangor University and Prof. Boris S. Luk'yanchuk from Lomonosov Moscow State University propose a new method of the electromagnetic field deep subwavelength localization based on truncated mesoscale dielectric sphere or cylinder.
It is well known that a spherical resonator cannot have an infinite Q factor due to the violation of the total internal reflection on a curved surface. Recently, many efforts have been made to increase the Q-factor of spherical and dielectric resonators using bound states in continuum. The article proposes a different approach to this topic. The removal of a surface feature in a Janus (since the focusing properties of such particles depend on the direction of incidence of radiation) particle plays a role similar to that of a diamond cut with a thousand times smaller. The removal of part of the particle leads to resonant amplification and localization of the field near the flat surface of the particle, which opens the way for elegant excitation of the WGM and an array of hot spots. The thickness of the cut particle at the resonant frequency differs from the well-known Weierstrass SIL criterion. On the example of cylindrical particles, it is shown that the optimization of this effect makes it possible to achieve superresolution (deep below the Rayleigh criteria) in line thickness. This effect can be used, in particular, for contact optical nanolithography.
Article reference Minin IV, Minin OV, Cao YH, Yan B, Wang ZB et al. Photonic lenses with whispering gallery waves at Janus particles. Opto-Electron Sci 1, 210008 (2022) . doi: 10.29026/oes.2022.210008
Keywords: photonics / whispering gallery mode / whispering gallery waves / Janus particles
