Analysis of a photonic nanojet assuming a focused incident beam instead of a plane wave

Abstract

The analysis of a photonic nanojet formed by dielectric spheres almost always assumes that the incident field is a plane wave. In this work, using vector spherical harmonics representations, we analyze the case of a more realistic incident field consisting of a focused beam formed by a microscope objective. Also included is the situation in which the sphere is not at the focal plane of the focus beam. We find that the dimension of the nanojet beam waist is less sensitive with respect to the azimuthal angle when compared with the plane wave case. Also, by shifting the particle away from the focal plane, the nanojet beam waist can be positioned outside the particle which otherwise would be inside or at the particle surface. Inherently, no such adjustment is possible with an incident plane wave assumption.

Geometric effect on photonic nanojet generated by dielectric microcylinders with non-cylindrical cross-sections

“…At b/d¼2, the length of photonic nanojet is about 10 times of the incident wavelength that indicates the elliptical microcylinder can operate in long working distance with very low divergence. When the elliptical microcylinder combined with a conventional optical microscope is used in nano-scale imaging, the light source through a microscope objective is a Gaussian beam instead of plane wave [39]. In this system, the FWHM of photonic nanojet is expected to decrease because the elliptical microcylinder could converge the incident beam further.…”

Photonic Nanojets and Whispering Gallery Modes in Smooth and Corrugated Micro-Cylinders under Point-Source Illumination

“…In Ref. [18], the authors investigated the formation of photonic nanojets resulting from dielectric spheres illuminated by a focused beam. It is shown that the dimension of the jet beam waist is less sensitive when compared with plane-wave illumination.…”