2D and 3D light confinement with dielectric microspheres

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Light scattering by dielectric particles is a fundamental problem in electromagnetism. The most famous study was performed more than one century ago by Gustav Mie 1908. It may seem surprising to study this problem today, but as you will see below, this basic optical component revealed unexpected properties. Let us mention that this work was carried out in close collaboration with the Mosaic team.

Photonic jets
Dielectric microspheres illuminated by a non focused beam can offer a particular focused beam called "photonic jet". This beam is characterized by a transverse dimension smaller than the wavelength of the illuminating beam combined with a very low divergence. We analytically studied the spectral properties of this beam, and we also worked with the Mosaic team of the Institut Fresnel to image for the first time this so-called photonic jet.

A. Devilez, B. Stout, N. Bonod, E. Popov, “Spectral analysis of three-dimensional photonic jets,” Opt. Express 16, 14200-14212 (2008)
P. Ferrand, J. Wenger, A. Devilez, M. Pianta, B. Stout, N. Bonod, E. Popov, and H. Rigneault, “Direct imaging of photonic nanojets,” Opt. Express 16, 6930-6940 (2008)

3D confinement of light with a single dielectric microsphere
Dielectric microspheres are capable of confining light in a three-dimensional region of subwavelength dimensions when they are illuminated by tightly focused Gaussian beams. We show that this three- dimensional confinement arises from interferences between the field scattered by the sphere and the incident Gaussian beam containing high angular components.

A. Devilez, N. Bonod, J. Wenger, D. Gerard, B. Stout, H. Rigneault, E. Popov, “Three-dimensional confinement of light with dielectric microspheres,” Opt. Express 17, 2089-2094 (2009)
A. Devilez, J. Wenger, B. Stout, N. Bonod, “Transverse and longitudinal confinement of photonic nanojets by compound dielectric microspheres,” Proc. SPIE 7393, Nanophotonic materials VI, San Diego (2009)

Application to FCS with the Mosaic team
A dielectric microspheres illuminated by a tightly focused Gaussian beam able to focus light on a tiny spot with subwavelength dimensions along the three directions of space is used to incrase the excitation intensity sensed by fluorescent organic molecules and to redirect the light emitted at large incidences toward the optical axis.

D. Gerard, A. Devilez, H. Aouani, B. Stout, N. Bonod, J. Wenger, E. Popov, H. Rigneault, “Efficient excitation and collection of single-molecule fluorescence close to a dielectric microsphere,” J. Opt. Soc. Am. B 26, 1473-1478 (2009)
D. Gerard, J. Wenger, A. Devilez, D. Gachet, B. Stout, N. Bonod, E. Popov, H. Rigneault, “Strong electromagnetic confinement near dielectric microspheres to enhance single-molecule flurorescence,” Opt. Express 16, 15297-15303 (2008)

2007-2009 : PEPS Nanodrill granted by the french center for scientific research (CNRS)