Nanophotonics

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Nanophotonics Class 8 Near-field optics
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Resolution in microscopy
Why is there a barrier in optical microscopy
resolution?
And how can it be broken?
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Angular spectrum and diffraction limit
Describe field as superposition of plane waves
(Fourier transform)
Field at z0 (object) propagates in free space as
The propagator H is oscillating for and
exponentially decaying for
High spatial fluctuations do not propagate
diffraction limit
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The diffraction limit in conventional microscopy
Image of a point source in a microscope,
collecting part of the angular spectrum of the
source
Rayleigh criterion two point sources
distinguishable if spaced by the distance between
the maximum and the first minimum of the Airy
pattern
q

Numerical Aperture determines resolution
Airy pattern (microscope point spread function)
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Breaking the diffraction limit in near-field
microscopy
A small aperture in the near field of the source
can scatter also the evanescent field of the
source to a detector in the far field.
Image obtained by scanning the aperture
Alternatively, the aperture can be used to
illuminate only a very small spot.
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Probing beyond the diffraction limit
Single emitter
Metallic particle
Aperture probe fibre type
Aperture probe microlever type
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Modified slide from Kobus Kuipers and Niek van
Hulst et al.
Transmission of light through a near-field tip
200 nm
Excitation light
Al
NSOM probe
FIB treated probe Aperture 20-100 nm
Protein, dendrimer, DNA, etc.
single fluorophores
Fluorescence
Thin polymer film, self-assembled monolayer, cell
membrane, etc.
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Focussed ion beam (FIB) etched NSOM probe
l

• well defined aperture
• flat endface
• isotropic polarisation
• high brightness up 1 mW

35 nm aperture
100 nm
glass
100 nm
With excitation Ex , kz,
aluminum
y
500 nm
x
Ex
Ey
Ez
Veerman, Otter, Kuipers, van Hulst, Appl. Phys.
Lett. 74, 3115 (1998)
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Shear force feedback molecular scale topography
Steps on graphite (HOPG)
Feedback loop
A0
Df
piezo
3 x 3 mm
0.8 nm step 3 mono-atomic steps
w0
Tuning fork 32 kHz Q 500
DNA on mica
Lateral movement, A0 0.1 nm
sample
DNA width 14 nm height 1.4 nm
Feedback on phase Tip -sample lt 5 nm RMS 0.1 nm
Rensen, Ruiter, West, van Hulst, Appl. Phys.
Lett. 75 1640 (1999) Ruiter, Veerman, v/d Werf,
van Hulst, Appl. Phys. Lett. 71 28 (1997) van
Hulst, Garcia-Parajo, Moers, Veerman, Ruiter, J.
Struct. Biol. 119, 222, (1997)
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Perylene orange in PMMA
1 mm
Ruiter, Veerman, Garcia-Parajo, van Hulst, J.
Phys. Chem. 101 A, 7318 (1997)
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Single molecular mapping of the near-field
distribution
DiIC18 molecules in 10 nm PMMA layer 1.2 x 1.2
mm2 3 nm/pix 3 ms/pix
120
45 nm FWHM
80
counts / pixel
40
0
0
400
800
1200
distance (nm)
Veerman, Garcia-Parajo, Kuipers, van Hulst, J.
Microscopy 194, 477 (1999)
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Data from Kobus Kuipers and Niek van Hulst et al.
Mapping the near field of the probe
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NFO for Single Molecule Detection Reduced
excitation volume, high resolution, low
background
Single DiD molecule in 30 nm polystyrene with 70
nm aperture probe
van Hulst, Veerman, Garcia-Parajo, Kuipers. J.
Chem. Phys. 112, 7799 (2000)
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Optical discrimination of individual molecules
separated by nm mutual distance
Sample area 440 x 440 nm2 Aperture diameter 70
nm Mutual distance lt 10 nm
van Hulst, Veerman, Garcia-Parajo, Kuipers. J.
Chem. Phys. 112, 7799 (2000)
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Data from Kobus Kuipers and Niek van Hulst et al.
Time-resolved near-field scanning tunneling
microscopy
120 fs pulses coupled into the PhCW
Two arms of the interferometer equal in length
gives temporal overlap on the detector
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Data from Kobus Kuipers and Niek van Hulst et al.
A light pulse caught in time and space
40 nm high ridge waveguide
239.5 x 7.62 mm
Pulse envelope
239.5 x 7.62 mm
Fixed time delay
TE00 pulse, l 1300 nm duration 120 fs
Pulse caught in 1 position
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Nanophotonics class schedule Class 1 -
Resonances and refractive index Class 2 -
Nanoparticle scattering Class 3 - Surface plasmon
polaritons Class 4 - Photonic crystals Class 5 -
Local density of optical states Class 6 Rare
earth ions and quantum dots Class 7
Microcavities Class 8 - Nanophotovoltaics Class
9 - Metamaterials Class 10 Near-field optics
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Class schedule Class 1 - Resonances and
refractive index Class 2 - Nanoparticle
scattering Class 3 - Surface plasmon
polaritons Tour through Ornstein Lab Homework
assistance Class 4 - Photonic crystals Class 5 -
Local density of optical states Excursion to
AMOLF-Amsterdam Class 6 Rare earth ions and
quantum dots Class 7 Microcavities Visit to
Nanoned conference Class 8 - Near field
optics Class 9 - Nanophotovoltaics Excursion to
Philips Research- Eindhoven Class 10 -
Metamaterials Class 11 Near-field
optics Nanophotonics summary Closing symposium