Light concentration in the near-field of dielectric spheroidal particles with mesoscopic sizes

Abstract

This paper presents a numerical study of the light focusing properties of dielectric spheroids with sizes comparable to the illuminating wavelength. An analytical separation-of-variables method is used to determine the electric field distribution inside and in the near-field outside the particles. An optimization algorithm was implemented in the method to determine the particles' physical parameters that maximize the forward scattered light in the near-field region. It is found that such scatterers can exhibit pronounced electric intensity enhancement (above 100 times the incident intensity) in their close vicinity, or along wide focal regions extending to 10 times the wavelength. The results reveal the potential of wavelength-sized spheroids to manipulate light beyond the limitations of macroscopic geometrical optics. This can be of interest for several applications, such as light management in photovoltaics. , 2001). 23. S. Asano and G. Yamamoto, -Light scattering by a spheroidal particle,‖ Appl. Opt. 14(1), 29-49 (1975). 24. E. M. Purcell and C. R. Pennypacker, -Scattering and absorption of light by nonspherical dielectric grains,‖ Astrophys. J. 186(2), 705-714 (1973). 25. J. C. Ravey and P. Mazeron, -Light-scattering in the physical optics approximation-application to large spheroids,‖ J. Opt. 13(5), 273-282 (1982). 26. J. P. Barton, -Internal, near-surface, and scattered electromagnetic fields for a layered spheroid with arbitrary illumination,‖ Appl. Opt. 40(21), 3598-3607 (2001). 27. N. Richard, -Analysis of polarization effects on nanoscopic objects in the near-field optics,‖ Phys. Rev. E Stat. ©2011 Optical Society of AmericaNonlin. Soft Matter Phys. 63(2), 026602 (2001). 28. J. P. Barton, -Internal and near-surface electromagnetic fields for an absorbing spheroidal particle with arbitrary illumination,‖ Appl. Opt. 34(36), 8472-8473 (1995).

Photonic jet generated by spheroidal particle with Gaussian-beam illumination

“…For the small refractive index contrasts, between the particle and the surrounding medium, the prolate spheroids (a∕b > 1) therefore yield stronger focalizations and narrower photonic jets, but shorter longitudinal waists than the various realizations of the oblate ones (a∕b < 1). For the high relative refractive index, the maximum focal strengths outside the particles would be achieved with oblate spheroids [47]. It may be advantageous to choose a jet-producing particle to obtain the photonic jet with the desired properties in application.…”

“…The size and shape of the spheroid can be easily controlled to high precision in the fabrication process. Mendes et al investigated the light focusing properties of wavelength-sized spheroids [46] and dielectric spheroids with mesoscopic sizes [47] under plane-wave illumination. Later, Liu [48] investigated the localized elongated photonic jet generated by a graded-index microellipsoid illuminated by a plane wave, using highresolution finite-difference time-domain simulation.…”

Characterization of photonic nanojets in dielectric microdisks

“…The critical properties of photonic nanojet are that it is a non-evanescent wave and propagating lightwave with low divergence and smallest waist smaller than diffraction limit. Then, many scientists investigate the generating mechanism of photonic nanojet and the effects of the physical parameters of microsphere or microcylinder on photonic nanojet [4][5][6][7][8]. Under theoretical demonstrations, the photonic nanojets appear as elongated and narrow spots with a high intensity of electromagnetic radiation, if dielectric spherical media are well illuminated [9][10][11].…”

Colloidal crystals by electrospraying polystyrene nanofluids

“…Mono- and multilayers of nanospheres have a huge number of promising electrical and optical applications [11-14]; some benefiting from the high surface-to-volume ratio to, for example, foster a new generation of ultrafast bulk battery electrodes [15], scaffolds of macroporous materials [16,17], while others benefit from the dimension of the periodicity of three-dimensional (3D) structures making them suitable for photonic [18-20] or terahertz applications [21]. …”