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2D FOCUSING OF LIGHT2D FOCUSING OF LIGHT-- towardstowards subdiffractionsubdiffraction limited imaginglimited imaging --
AlexandruAlexandru BratuBratu, James Rice and Brian, James Rice and Brian VohnsenVohnsen
School of Physics, University College Dublin,School of Physics, University College Dublin, Dublin 4, Ireland Dublin 4, Ireland
nificant progress has been made in the development of sub-diffraction fluorescence microscopy methods that enable images recorded in the far field to
ssess resolution down to the nanometer scale. Unfortunately they typically require point-by-point scanning or the accumulation of large data sets, which
events them from reaching real-time imaging applications. The application of new metamaterial lens technology holds promise for real-time imaging beyond
e diffraction limit of significant value for fluorescence microscopy. Here we outline theoretical work towards a superlens design that utilize Surface Plasmonaritons (SPPs). Ideally a specific arrangement of scattering structures can focus an incoming SPP wave in an essential first step towards the realization of a 2-D
bdiffraction-limited lens. We study the SPP scattering and propagation using SPP in-plane scattering based on a Green’s function propagator formalism.
entually, our aim is to convert this theoretical proposal into a workable experimental lens for fluorescent microscopy.
BackgroundBackground Circular shellsCircular shells
bdiffraction-limited imaging relies on evanescent waves by localized
tection and scanning, by optically-driven localization or by the use of
gative refraction effects with potential for a perfect lens [1].
SPP scattering in a semi-circular (=pi) arrangement of particles:
|Emax|
3 semi-circles (4,7,10 particles) 5 semi-circles (4,7,10,13,16 particles)
|Emax|=1.84 |Emax|=2.39
) (b) (c)
Poster A4
2D focusing of an SPP2D focusing of an SPP Elliptical shellsElliptical shells
Schematic of subdiffraction limited (a) scanning microscopy (e.g., near-field SNOM or depletion STED),
(b) localization microscopy (STORM and PALM), (c) perfect lens design with evanescent wave recovery.
anning near-field optical
microscopy (SNOM)
r the realization of a (quasi) perfect lens SPPs are highly suited due to
e negative permittivity of the supporting metal. A layered structure can
cover evanscent waves [2] or negative refraction of a SPP wave [3] can
generate evanescent components carrying ultrahigh resolution to the
field. Phase conjugation of evanescent waves such as with near-field
lography can also increase the light confinement beyond the
ditional limit of diffraction [4].
Sequencial localization of (but
not resolving) fluorophores.
The group velocity of an SPP pulse on a gold film
|Emin|
λSPP
8λSPP
focus
Incident SPP
λSPP
16λSPP
focus
Incident SPP
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 2 4 6 8
|
||
|
E m a x | || |
a t f o c u s
Number of semi-circles
SPP scattering in a semi-elliptical (>pi) arrangement of particles:
0.0
0.5
1.0
1.5
2.0
2.5
| E |
1 3 5 semi-circles
10λSPP
λSPP/2
n1
=1 n1
=1n2
=-1
Contact: [email protected]: [email protected] 07/SK/B1239aStokes 07/SK/B1239a
PI award 08/IN.1/B2053PI award 08/IN.1/B2053
RFP award 09/RFP/PHY2398RFP award 09/RFP/PHY2398 PC/2008/125PC/2008/125
( ) ( )0 SPP SPP
1
( ) 1 exp4
N
j
j
i E H i z
=
α= + β − β
∑ r r r
stic SPP scattering model used for the field E at point r :
SPP wavenumber: βSPP
ReferencesReferences[1] J.B. Pendry, Negative refraction makes a perfect lens, Phys. Rev. Lett. 85 (2000) 3966
[2] Z. Liu et al , Far-field optical hyperlens magnifying sub-diffraction-limited objects, Science
315 (2007) 1686
[3] I.I. Smolyaninov et al , Magnifying superlens in the visible range, Science 315 (2007) 1699
[4] B. Vohnsen & S.I. Bozhevolnyi, Holographic approach to phase conjugation of optical near
fields, J. Opt. Soc. Am. A 14 (1997) 1491
t roug PMMA is inverte wit respect to t e p ase
velocity and thus evanescent components may be
restored. This has been used to transfer subdiffraction-
limited resolution to the far field [3]. A requirement for
this to happen is that the following condition is satisfied:
n1d
1= - n
2d
2for the metallic film of effective index n
1and
width d 1 and PMMA of effective index n2and width d 2.
10λSPP
focus
Incident SPP
1 parabolic shell (of 10 particles)
f =2λSPP
|E
max|=1.44
10λSPP
focus
Incident SPP
3 parabolic shells (of 10 particles)
f =2λSPP
|Emax
|=2.12
|Emax|
|Emin|
Predicted focal spot for a parabolic arrangement is improved when compared to a semi-circular design.
Particle polarizability: α
d 1d 2 d 2d 1
n1n2n1n2n1
a first step, we consider the design of lenses for 2D focusing of SPPs.
e model employs an arrangement of dipolar elastic scattering elements
a metallic film supporting SPPs. The arrangement resembles a planar
rror focusing the field in a high numerical aperture arrangement.
Hankel function: H 0
Incident SPP
