From apertureless near-field opticalmicroscopy to

infrared near-field night vision

Yannick DE WILDE

ESPCI – Laboratoire d’Optique PhysiqueUPR A0005-CNRS, PARISdewilde@optique.espci.fr

Collaborators :Theory & Modelisation :

J.-J. GreffetR. Carminati

K. Joulain (ENSMA)B. Gralak (I. Fresnel)

Samples preparation :

Y. Chen(LPN-Marcoussis)

D. CourjonC. Bainier(LOPMD)

Experimentation :

F. FormanekP-A. Lemoine

From apertureless near-field opticalmicroscopy to

infrared near-field night vision

Edet= Etip + Espec. + Ebkg.

Vertical oscillation of the tip

Apertureless SNOM : Principle

- To extract Etip(ω) from the background

- Surface topography ( AFM, « tapping »mode )

Piezo ( XY )

Illumination

DetectorLock-indetection

Modulation

ω

ω

Edet= Etip (ω) + Espec.+ Ebkg.

Apertureless SNOM based on a quartz tuning fork

0.4mm

Tip(tungsten)

Electrode BElectrode A

A-

B+

Vertical oscillation"Tapping mode"

Oscillationamplitude

z-feedback

Topography

}

Quartz tuning fork

Tip : MEB image

1 µm

PZT plate(excitation)

Apertureless SNOM based on a quartz tuning fork

Scan range (XY) : 34 µm x 34 µmVertical range (Z) : 17 µmAFM resolution :

- vertical ~ 1 nm- lateral ~ 20-50 nm

Y. De Wilde, F. Formanek, L. Aigouy, Rev. Sci. Instrum. 74, 3889 (2003)

Apertureless SNOM with visible or infraredlaser illumination : experimental set-up

SUBWAVELENGTH HOLES (φ=200nm) : INFRARED imaging

SNOM (3µmx3µm) Infrared illumination λ=10,6 µm

AFM

Optique

Microscopie électronique(C. Bainier et D. Courjon)Microscopie électronique(C. Bainier et D. Courjon)

1.18 µm

1.21 µm

1.18 µm1.18 µm

1.21 µm1.21 µm

AFM (topography)

AFM (Profile)

Optical resolution ~ 30 - 50 nm~ λ/200

Formanek, De Wilde, Aigouy, J. Appl. Phys. 93, 9548 (2003)

GDR Optique de champ procheAppl. Optics 42, 691 (2003)

Apertureless SNOM with visible or infraredlaser illumination : experimental results

• Screen with subwavelength holeOriginal idea

Synge, Phylos. Mag. 6, 356 (1928)

• Aperture SNOM Pohl, …, Appl. Phys. Lett 44, 651 (1984)

• Scattering tip (apertureless) SNOM Zenhausern, Appl. Phys. Lett. 65, 1623 (1994)

A ‘regular’ SNOM requires 3 basic ingredients :

Source-Probe-Detector

External source

Sub-λ probe

Detector

Near-field optics without external illumination

New concept :

SNOM WITHOUT EXTERNAL SOURCE

SUBMITTED FOR PUBLICATION

SiC + grating

T=500°C

J.-J. Greffet et al., Nature 416, 61 (2002)

SiC = polar material which supports surface waves known as surface phonon-

polaritons=> Evanescent waves thermally stimulated

Diffraction

Coherent thermal emission

SiC SiC

Surface waves in silicon carbide (SiC)

Surface waves in silicon carbide (SiC)

SiC

Enhanced electromagnetic energydensity in near-field zone

Good first candidate !

Shchegrov, Joulain, Carminati, Greffet, PRL. 85, 1548 (2000)

Ener

gyde

nsity

Ener

gyde

nsity

Ener

gyde

nsity

= 10.55 µm2πcωpk

Probing the local electromagneticdensity of states (EM-LDOS)

• EM -LDOS : ρ(r,ω)dr : Probability to find a photon ħω in r in a small

volume dr.• Local density of electromagnetic energy :

( )1(r, ) (r, )

exp / 1U

kTω ρ ω ω

ω=

−h

h

EM-LDOS Energy of 1 photon N. Photons / state

But : Spatial variations of ρ(r,ω) are expected nearan interface (evanescent modes, plasmons, phonon-polaritons, …) or in photonic structures.

Vacuum : ρ(r,ω) =2

2 3cω

πHomogeneous, isotropic

Probing the local electromagneticdensity of states (EM-LDOS)

Laser

Fibre étirée

Détection sur 4π

Echantillon

Laser

Fibre étirée

Détection sur 4π

Laser

Fibre étirée

Détection sur 4π

Echantillon

C. Chicanne, T. David, R. Quidant, J. C. Weeber, Y. Lacroute, E. Bourillot, A. Dereux, G. Colas des Francs and C. Girard, Phys. Rev. Lett. 88, 097402 (2002)

Optical fiber

Sample

Detection (4π)

Corral structure

Probing the local electromagneticdensity of states (EM-LDOS)

Tip

Sample (T ≠ 0)

DetectorAt T≠0, all available states are occupied,

according to Bose-Einstein statistics

A point-like SNOM probes the EM-LDOS

Joulain, Carminati, Mulet, Greffet, PRB 68,245405 (2003)

Conclusions :• SNOM which operates with visible or infrared laser illumination

• SNOM without laser :- Detects the infrared near-field thermal radiation

« Near-field infrared night-vision camera »- Observation of near-field coherence effects on gold patterns on SiC

- Probes the EM-LDOS => Behaves as an « infrared STM » (IRSTM)