Connection Symposium
Meta-Screen for High Resolution Optical
Microscopy
Yan Wang*, Amr S. Helmy, & George V. Eleftheriades
University of Toronto
May 8, 2009
Toronto, ON
Connection Symposium
Overview
• Background
– Conventional optical microscope and its resolution limit;
– Development in various high resolution microscopy
technologies and their pros and cons.
• Scanning near-field optical microscopy (SNOM)
– Basic operating principles and drawbacks.
• Theory of meta-screen
– Improves the current SNOM resolution;
– Design principles and performances;
• Conclusion
May 8, 2009
Toronto
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Connection Symposium
Background
• Optical microscopy – seeing things with light
– Conventional compound optical microscopes
Eyepiece lens
Focus
Objective Lens
Stage (with clips)
Mirror
An 1879 Carl Zeiss Jena Optical
microscope
May 8, 2009
Nikon Eclipse 600 transmitted/reflected
light microscope
Toronto
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Background (cont’d)
Connection Symposium
• Resolution limit of conventional optical microscopes
– Abbey’s diffraction limit (200nm for the visible spectrum)
x
z
Propagating waves: e-jβz
Evanescent waves: e-αz
Spectrum of the spatical information
-k0
May 6, 2010
k0
Toronto
kx
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Connection Symposium
Background (cont’d)
• Efforts in achieving high-resolution (beyond the diffraction limit)
• Electron microscope (TEM, SEM and REM etc.)
• Atomic force microscope (AFM)
Jason Palmer, BBC news, Friday, 28 August 2009, “Single molecules stunning image”
• Pendry’s “perfect lens” (meta-material application)
J.B. Pendry, “Negative refraction makes a perfect lens” Phys. Rev. Lett. 85, 18 (2000).
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Connection Symposium
SNOM
• Scanning near-field optical microscope
WiTech alpha300S Scanning Near-field Optical Microscope, ϋlm, Germany
Aperture probe limits resolution
–
–
–
Operates in the near-field
Does not depend on the wavelength of
the illuminating light
Suffers tremendous power loss
Human leucocyte
May 6, 2010
Toronto
SPP propagation
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Connection Symposium
Meta-screen
• Improve the focusing ability of the aperture (multi-aperture approach)
– Circular aperture vs. slot aperture
Bethe’s diffraction theory
 
transmission  r 
Slot antenna theory
4
– Single-slot vs. multi-slot
L. Markley et. al., “A spatially
shifted beam approach to
subwavelength focusing,”
Phys. Rev. Lett. 101, 10
(2008).
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Toronto
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Connection Symposium
Meta-screen
• Multi-slot metallic transmission screen (Meta-Screen)
x
y
x
z
Target Beamwidth
Transmission screen
FWHM = 0.12λ0
May 6, 2010
z
Weight = 1, -1/2, 1/5, -1/10, …
Toronto
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Connection Symposium
Meta-screen (cont’d)
• Meta-screen improves near-field focusing
Material: Ag (εr = -31.26-j1.14)
Thickness = 40nm, Slot width = 40nm
Central slot length = 200nm
Satellite slot length = 130nm
Slot separation distance = /10 = 83nm
Magnitude of Ex (log scale)
Magnitude of Ex (log scale)
Y. Wang et. al., “Plasmonic meta-screen for alleviating the trade-offs in the near-field optics ”, Optics
Express, 17, 12351-12361 (2009)
May 6, 2010
Toronto
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Connection Symposium
Thank you!