Connection Symposium

Toronto, ONMay 8, 2009

Meta-Screen for High Resolution Optical Microscopy

Yan Wang*, Amr S. Helmy, & George V. Eleftheriades

University of Toronto

Connection Symposium

Toronto 2May 8, 2009

Overview

• Background 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)Scanning near-field optical microscopy (SNOM)– Basic operating principles and drawbacks.

• Theory of meta-screenTheory of meta-screen– Improves the current SNOM resolution;– Design principles and performances;

• ConclusionConclusion

Connection Symposium Background

• Optical microscopy – seeing things with lightOptical microscopy – seeing things with light– Conventional compound optical microscopesConventional compound optical microscopes

Toronto 3May 8, 2009

An 1879 Carl Zeiss Jena Optical microscope

Mirror

Stage (with clips)

Objective Lens

Eyepiece lens

Focus

Nikon Eclipse 600 transmitted/reflected light microscope 

Connection Symposium Background (cont’d)

• Resolution limit of conventional optical microscopesResolution limit of conventional optical microscopes– Abbey’s diffraction limit (200nm for the visible

spectrum)

Propagating waves: e-jβz

x

z

k0-k0

kx

Spectrum of the spatical information

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Evanescent waves: e-αz

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Toronto 5May 6, 2010

Background (cont’d) (cont’d)

• Efforts in achieving high-resolution (beyond the diffraction Efforts in achieving high-resolution (beyond the diffraction limit)limit)

• Electron microscope (TEM, SEM and REM etc.)

• Atomic force microscope (AFM)

• Pendry’s “perfect lens” (meta-material application)

Jason Palmer, BBC news, Friday, 28 August 2009, “Single molecules stunning image”

J.B. Pendry, “Negative refraction makes a perfect lens” Phys. Rev. Lett. 85, 18 (2000).

Connection Symposium SNOM

• Scanning near-field optical microscope Scanning near-field optical microscope

Toronto 6May 6, 2010

WiTech alpha300S Scanning Near-field Optical Microscope, ϋlm, Germany

Human leucocyte SPP propagation

Aperture probe limits resolution– Operates in the near-field– Does not depend on the

wavelength of the illuminating light– Suffers tremendous power loss

Connection Symposium Meta-screen

Toronto 7May 6, 2010

• Improve the focusing ability of the aperture (multi-aperture Improve the focusing ability of the aperture (multi-aperture approach)approach)– Circular aperture vs. slot aperture

– Single-slot vs. multi-slot

L. Markley et. al., “A spatially shifted beam approach to subwavelength focusing,” Phys. Rev. Lett. 101, 10 (2008).

4

transmissionr

Bethe’s diffraction theory

Slot antenna theory

Connection Symposium Meta-screen

• Multi-slot metallic transmission screen (Meta-Screen)Multi-slot metallic transmission screen (Meta-Screen)

Toronto 8May 6, 2010

Target BeamwidthTarget Beamwidth

FWHM = 0.12λ0

Transmission screenTransmission screen

Weight = 1, -1/2, 1/5, -1/10, …

yxz

x

z

Connection Symposium Meta-screen (cont’d)

• Meta-screen improves near-field focusingMeta-screen improves near-field focusing

Material: Ag (εr = -31.26-j1.14)Thickness = 40nm, Slot width = 40nmCentral slot length = 200nmSatellite slot length = 130nmSlot separation distance = /10 = 83nm

Toronto 9May 6, 2010

Y. Wang et. al., “Plasmonic meta-screen for alleviating the trade-offs in the near-field optics ”, Optics Express, 17, 12351-12361 (2009)  

Magnitude of Ex (log scale) Magnitude of Ex (log scale)

Connection Symposium

Thank you!