Abstract

We demonstrate that microspheres above a substrate act as microscopic lenses. Their Brownian motion causes the focal point to change abruptly, thereby creating characteristic intensity fluctuations which depend on the interaction between the spheres. To this end, superparamagnetic spheres in a magnetic field assemble into long pearl chains, where the intensity fluctuations depend on the stiffness of the chain. Upon assembling the superparamagnetic beads into a two-dimensional colloidal crystal, the fluctuations are restricted in two dimensions, and temporal network structures develop.

© 2004 Optical Society of America

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References

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Adv. Colloid. Interfac. (1)

D.C. Prieve, �??Measurments of colloidal forces with TIRM,�?? Adv. Colloid. Interfac. 82, 93�??125 (1999).
[CrossRef]

Appl. Phys. Lett. (7)

J.N. Anker and R. Kopelman, �??Magnetically modulated optical nanoprobes,�?? Appl. Phys. Lett. 82, 1102�??1104 (2003).
[CrossRef]

C.J. Behrend, J.N. Anker and R. Kopelman, �??Brownian modulated optical nanoprobes,�?? Appl. Phys. Lett. 84, 154 (2004).
[CrossRef]

D.W. Pohl, W. Denk and M. Lanz, �??Optical stethoscopy: Image recording with 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]

M.H. Wu and G.M. Whitesides, �??Fabrication of arrays of two-dimensional micropatterns using microspheres as lenses for projection photolithography,�?? Appl. Phys. Lett. 78, 2273�??2275 (2001).
[CrossRef]

M. Sasaki, T. Kurosawa and K. Hane, �??Micro-objective manipulated with optical tweezers,�?? Appl. Phys. Lett. 70, 785�??787 (1996).
[CrossRef]

J.P. Brody and S.R. Quake, �??A self-assembled microlensing rotational probe,�?? Appl. Phys. Lett. 74, 144�??146 (1999).
[CrossRef]

Electronics Letters (1)

M. Oikawa, K. Iga and T. Sanada �??Distribute-index planar microlens array prepared from deep electromigration,�?? Electronics Letters. 17, 452�??454 (1981).
[CrossRef]

Langmuir (1)

H. Takei and N. Shimizu, �??Gradient sensitive microscopic probes prepared by gold evaporation and chemisorption on latex spheres,�?? Langmuir 13, 1865�??1868 (1997).
[CrossRef]

Nano. Lett. (1)

J. Choi, Y. Zhao, D. Zhang, S. Chien and Y.H. Lo, �??Patterned fluorescent particles as nanoprobes for the investigation of molecular interactions,�?? Nano. Lett. 3, 995�??1000 (2003).
[CrossRef]

Optics Express (3)

Z. Chen, A. Taflove, V. Backman, �??Photonic nanojet enhancement of backscattering of light by nanoparticles: a potential novel visible-light ultramicroscopy technique,�?? Optics Express 12, 1214�??1220 (2004), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-7-1214">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-7-1214<a/>.
[CrossRef] [PubMed]

N. Chronis, G.L. Liu, K.H. Jeong and L.P. Lee, �??Tunable liquid-filled microlens array integrated with microfluidic network,�?? Optics Express 11, 2370�??2378 (2003), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-19- 2370">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-19- 2370<a/>.
[CrossRef] [PubMed]

J. Rosen and D. Abookasis, �??Seeing through biological tissue using the fly eye principle,�?? Optics Express 11, 605�??3611 (2003), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-26-3605">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-26-3605<a/>.
[CrossRef] [PubMed]

Phys. Rev. E (1)

L.E. Helseth, T.M. Fischer and T.H. Johansen, �??Paramagnetic beads surfing on domain walls,�?? Phys. Rev. E 67, 042401 (2003).
[CrossRef]

Other (1)

M. Born and E. Wolf, Principles of Optics (Cambridge University Press, UK, 1980).

Supplementary Material (1)

» Media 1: AVI (788 KB)     

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Figures (9)

Fig. 1.
Fig. 1.

A single bead focusing and collecting the light.

Fig. 2.
Fig. 2.

Intensity fluctuations of a single bead diffusing on top of a garnet surface.

Fig. 3.
Fig. 3.

(AVI 199 KB) Blinking chain above a glass slide in presence of a magnetic field of about 500 A/m (6 Oe).

Fig. 4.
Fig. 4.

Intensity fluctuations of three beads in a chain consisting of about 30 beads.

Fig. 5.
Fig. 5.

Chain above a glass slide in presence of a magnetic field of about 3000 A/m (38 Oe).

Fig. 6.
Fig. 6.

Schematic drawing of the beads moving toward the domain wall.

Fig. 7.
Fig. 7.

The intensity increases as the bead is getting closer to the domain wall.

Fig. 8.
Fig. 8.

(AVI 788 KB) Two dimensional colloidal crystal observed in reflection with crossed polarizers.

Fig. 9.
Fig. 9.

The real crystal structure observed in transmission mode (a) and its Fourier transform (b). The image also shows the inverted intensity distribution of the same structure seen in reflection mode a few seconds later (c) as well as its Fourier Transform (d).

Equations (4)

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h m = l D ( B l D G ) ,
f a 2 n w n b n w .
Δ r λ f 2 n w a ,
Δ z λ 2 ( f n w a ) 2 ,

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