Based on rigorous solutions of the
Maxwell's Equations, we recently discovered an optical phenomenon
called photonic nanojet, which refers to a local field enhancement
generated in the vicinity of a properly chosen microsphere or
microcylinder illuminated by a collimated light beam in the
visible wavelength range. Typically, a nanojet has a~100-200 nm waist and propagate
over several microns with little diffraction. In addition, A
remarkable property of photonic nanojets is that they can
significantly enhance the backscattering of light by
nanometer-scale particles located within the jets. They can be potentially
utilized for analyzing nanostructures.
Figure 1.
Evolution of photonic nanojet by increasing the refractive
index of dielectric micro-cylinder.
Figure 2. Simulation of a 20-nm gold
nanoparticle moving through a photonic nanojet while the
backscattering signal is recorded. We see that the nanoparticle generates a 40%
jump in the recorded backscattering signal at its peak
response.
We have been utilizing numerical methods
that solve the Maxwell Equations directly, including the
finite-different-time-domain method and generalized Mie theory, to
analyze and optimize the photonic nanojets , especially aiming for
the application of nanostructure characterization. We are also
currently investigating- the mechanism of the generation of the
photonic nanojets and their interaction with nanoparticles. Our
numerical and theoretical analysis will guide the experimental
implementation and practical application of this phenomenon.
Publications
1. Z. Chen, A. Taflove, and V. Backman,
"Photonic Nanojet Enhancement of Backscattering of Light by
Nanoparticles: a Potential Novel Visible-Light Ultramicroscopy
Technique", Optics Express, 12(7), 1214-1220
(2004).
2. X. Li, Z. Chen, A. Taflove, and V. Backman,
"Investigation of depth selectivity of polarization gating for
tissue characterization",Optics Express, Vol. 13 (2), pp. 526-533,
2005.
