1. Nanophotonics
Class 8
Near-field optics

2. Resolution in microscopy
Why is there a barrier in optical microscopy resolution?
And how can it be broken?

3. Angular spectrum and diffraction limit
Describe field as superposition of plane waves (Fourier transform):
Field at z=0 (object) propagates in free space as
The propagator H is oscillating for
and exponentially decaying for
High spatial fluctuations do not propagate: diffraction limit

4. + 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)

5. 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.

6. Probing beyond the diffraction limit
Single emitter
Metallic particle
Aperture probe
fibre type
Aperture probe
microlever type

7. self-assembled monolayer,
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 ~ nm
Protein, dendrimer, DNA, etc.
single fluorophores
Fluorescence
Thin polymer film,
self-assembled monolayer,
cell membrane, etc.

8. Focussed ion beam (FIB) etched NSOM probel
well defined aperture
flat endface
isotropic polarisation
high brightness up 1 mW
35 nm
aperture
100 nm
100 nm
glass
With excitation Ex , kz, :
aluminum y
500 nm x Ex Ey Ez
Veerman, Otter, Kuipers, van Hulst, Appl. Phys. Lett. 74, 3115 (1998)

9. Shear force feedback: molecular scale topography
Steps on graphite (HOPG)
Feedback loop: A0 Df
piezo
3 x 3 mm w0
~ 0.8 nm step
~ 3 mono-atomic steps
Tuning fork
32 kHz
Q ~ 500
Lateral
movement,
A0 ~ 0.1 nm
1.7 x 1.7 mm
DNA on mica
sample
DNA
width 14 nm
height 1.4 nm
Feedback on phase
Tip -sample < 5 nm
RMS ~ 0.1 nm
Rensen, Ruiter, West, van Hulst, Appl. Phys. Lett (1999)
Ruiter, Veerman, v/d Werf, van Hulst, Appl. Phys. Lett (1997)
van Hulst, Garcia-Parajo, Moers, Veerman, Ruiter, J. Struct. Biol. 119, 222, (1997)

10. Perylene orange in PMMA
100 nm
1 mm
90o 0o
Ruiter, Veerman, Garcia-Parajo, van Hulst, J. Phys. Chem. 101 A, 7318 (1997)

11. 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
400
800
1200
distance (nm)
Veerman, Garcia-Parajo, Kuipers, van Hulst, J. Microscopy 194, 477 (1999)

12. Mapping the near field of the probe
Data from Kobus Kuipers and Niek van Hulst et al.
Mapping the near field of the probe

13. NFO for Single Molecule Detection : Reduced excitation volume,
high resolution,
low background
0.0
0.5
1.0
1.5
2.0
2.5
3.0 10 20 30 40 50
kcounts/s
lateral scan [mm]
FWHM = 75 nm
S/B  20
Single DiD molecule in
30 nm polystyrene
with
70 nm aperture probe
van Hulst, Veerman, Garcia-Parajo, Kuipers. J. Chem. Phys. 112, 7799 (2000)

14. Optical discrimination of individual molecules separated by
emission
45 ± 2 nm 0o a b c
200
400 nm
Optical discrimination of
individual molecules
separated by
nm mutual distance a b c d e
Sample area: 440 x 440 nm2
Aperture diameter: 70 nm
Mutual distance: < 10 nm
van Hulst, Veerman, Garcia-Parajo, Kuipers. J. Chem. Phys. 112, 7799 (2000)

15. Time-resolved near-field scanning tunneling microscopy
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

16. Pulse caught in 1 position
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

18. 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

19. 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