Abstract

We report what we believe to be the first evidence of localized nanoscale photonic jets generated at the shadow-side surfaces of micron-scale, circular dielectric cylinders illuminated by a plane wave. These photonic nanojets have waists smaller than the diffraction limit and propagate over several optical wavelengths without significant diffraction. We have found that such nanojets can enhance the backscattering of visible light by nanometer-scale dielectric particles located within the nanojets by several orders of magnitude. Not involving evanescent fields and not requiring mechanical scanning, photonic nanojets may provide a new means to detect and image nanoparticles of size well below the diffraction limit. This could yield a potential novel ultramicroscopy technique using visible light for detecting proteins, viral particles, and even single molecules; and monitoring molecular synthesis and aggregation processes of importance in many areas of biology, chemistry, material sciences, and tissue engineering.

© 2004 Optical Society of America

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References

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Appl. Opt. (1)

Appl. Phys. Lett. (2)

D. W. Pohl, W. Denk, and M. Lanz, �??Optical stethoscopy: Image recording with resolution λ/20,�?? Appl. Phys. Lett. 44, 651-653 (1984).
[CrossRef]

S. M. Mansfield and G. S. Kino, �??Solid immersion microscope,�?? Appl. Phys. Lett. 57, 2615-2616 (1990).
[CrossRef]

Biophys. J. (1)

E. Betzig, A. Lewis, A. Harootunian, M. Isaacson, and E. Kratschmer, �??Near-field scanning optical microscopy (NSOM): Development and biophysical applications,�?? Biophys. J. 49, 269-279 (1986).
[CrossRef] [PubMed]

Chem. Rev. (1)

B. Dunn, �??Near-field scanning optical microscopy,�?? Chem. Rev. 99, 2891-2928 (1999).
[CrossRef]

J. Comput. Phys. (1)

J.-P. Berenger, �??A perfectly matched layer for the absorption of electromagnetic waves,�?? J. Comput. Phys. 114, 185-200 (1994).
[CrossRef]

J. Opt. Soc. Am. A (3)

J. Sel. Top. Quant. Elect. (1)

B. B. Goldberg, S. B. Ippolito, L. Novotny, Z. Liu, and M. S. �?nlü, �??Immersion lens microscopy of photonic nanostructures and quantum dots,�?? IEEE J. Sel. Top. Quant. Elect. 8, 1051-1059 (2002).
[CrossRef]

Opt. Lett. (2)

Phys. Rev. Lett. (1)

E. J. Sanchez, L. Novotny, and X. S. Xie, �??Near-field fluorescence microscopy based on two-photon excitation with metal tips,�?? Phys. Rev. Lett. 82, 4014-4017 (1999).
[CrossRef]

Science (1)

E. Betzig and J. K. Trautman, �??Near-field optics: Microscopy, spectroscopy, and surface modification beyond the diffraction limit,�?? Science 257, 189-195 (1992).
[CrossRef] [PubMed]

Ultramicroscopy (2)

A. Lewis, M. Isaacson, A. Harootunian, and A. Muray, �??Development of a 500�? resolution microscope,�?? Ultramicroscopy 13, 227-231 (1984).
[CrossRef]

L. Novotny, E. J. Sanchez, and X. S. Xie, �??Near-field optical imaging using metal tips illuminated by highorder Hermite-Gaussian beams,�?? Ultramicroscopy 71, 21-29 (1998).
[CrossRef]

Other (2)

A. Taflove and S. Hagness, Computational Electrodynamics: The Finite-Difference Time-Domain Method (Artech, Boston, MA, 2000).

C. F. Bohren and D. R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley, New York, 1983).

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Figures (4)

Fig. 1.
Fig. 1.

Evolution of a photonic nanojet as the refractive index of a plane-wave-illuminated circular dielectric cylinder decreases. The FDTD-calculated envelope of the sinusoidal steady-state electric field is visualized for a d=5 µm circular cylinder of uniform refractive index n 1 embedded within an infinite vacuum medium of refractive index n 2=1.0. Light of wavelength λ 2=500 nm propagates from left to right in medium 2. (a) n 1=3.5; (b) n 1=2.5; (c) n 1=1.7.

Fig. 2.
Fig. 2.

Generation of photonic nanojets similar to that in Fig. 1(c) for three different combinations of d, n 1, n 2, and λ 2 : (a) d=5 µm, n 1=3.5, n 2=2.0, λ 2=250 nm; (b) d=6 µm, n 1=2.3275, n 2=1.33, λ 2=300 nm; (c) d=10 µm, n 1=2.3275, n 2=1.33, λ 2=300 nm.

Fig. 3.
Fig. 3.

FDTD numerical results illustrating photonic nanojet enhanced backscattering of light by dielectric nanoparticles. The parameter set of Fig. 2(b) (d=6 µm, n 1=2.3275, n 2=1.33, and λ 2=300 nm) is assumed. A square, n=1.5 dielectric nanoparticle of side dimension s is inserted at the center of the photonic jet on the surface of the 6-µm cylinder. (a) Absolute value of the change of the differential scattering cross section within ±10° of backscatter for s=5 nm compared with the differential scattering cross section of the isolated nanoparticle. (b) Repeated studies of (a) for a nanoparticle of side dimension s=10 nm.

Fig. 4.
Fig. 4.

FDTD numerical results illustrating backscattering enhancement factor as a function of side dimension s of nanoparticles. The parameter set of Fig. 2(b) (d=6 µm, n 1=2.3275, n 2=1.33, and λ 2=300 nm) is assumed. A square, n=1.5 dielectric nanoparticle of side dimension s is inserted at the center of the photonic jet on the surface of the 6-µm cylinder.

Equations (2)

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f = a ( 1 ) p ( 2 p 1 n 1 )
f = a n 1 [ 2 ( n 1 1 ) ]

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