Download Micromanipulating optically trapped particles with photonic crystal

Supplementary information:
On chip shapeable optical tweezers
C. Renaut1,2,3, B. Cluzel1,*, J. Dellinger1, L. Lalouat1, E. Picard2, D. Peyrade3, E. Hadji2 and F.
de Fornel1
1. Groupe d’Optique de Champ Proche - LRC CEA n°DSM-08-36, Laboratoire Interdisciplinaire
Carnot de Bourgogne. UMR CNRS 6303- Université de Bourgogne, France
2. SiNaPS lab. / SP2M, UMR-E CEA / UJF-Grenoble1, INAC, Grenoble, F38054, France
3. CNRS / UJF-Grenoble1 / CEA LTM, 17 rue des Martyrs, 38054 Grenoble cedex9, France
*[email protected]
Address: Groupe d’optique de champ proche - LRC CEA n°DSM-08-36, Laboratoire
Interdisciplinaire Carnot de Bourgogne. UMR CNRS 6303 - Université de Bourgogne, 9 Av.
Alain Savary, BP 47870 F-21078 DIJON Cedex, FRANCE
Supplementary section 1| Particles sensing using a laterally coupled
cavity.
As shown on Fig. 1 S1. a, we measured the transmittance spectra of laterally coupled cavity in
air and in the colloidal solution. The colloidal solution consists in polystyrene microspheres of
1 µm diluted in water with an average of 3.3 108 part/mL. The coupled structure exhibits two
resonances whether in air or in the particles solution. The experimental results presented on
Fig. S1. a properly agree with the transmittance spectra on Fig. 1 S1. b calculated by three
dimensional finite difference time domain method (3D FDTD).
Figure 1 supplementary section 1| Spectra of the coupled cavity. a,
Experimental spectra obtained in air (blue) and in the colloidal solution (black). b,
Three dimensional FDTD simulations of the corresponding transmittance spectra in
air (blue) and in the colloidal solution (black).
The near-field observations of the coupled cavity are made by using a scanning near-field
optical microscopy (SNOM) operating in interaction scanning mode1. The near-field probe
consists in a pulled silica fibre tip with a 20 nm width apex. The SNOM probe was scanned at
4 nm above the surface thanks to a shear force feedback. In the interaction scanning mode
used here, the near-field images are directly comparable to the distribution of electric field
intensity of the resonant mode at the measurement wavelength2. Note that we focus our
attention hereafter on the upper wavelength resonance used for sensing. The SNOM picture is
presented in Fig. 2 S1 a and it is compared to resonant mode electric field intensity
distribution computed in water by 3D FDTD (Fig. 2 S1 b). A good agreement is achieved
between SNOM measurement and FDTD calculations. More importantly, since the
experimental field map is equally distributed in the two cavities, it implies that the two
nanocavities are perfectly coupled. Then, we computed by 3D FDTD the electric field
distribution of this resonant mode with a 1 µm polystyrene particle centred on one of the
nanocavity (Fig. 2 S1 c). The resonant field perturbed by the presence of the particle is
weakly modified indicating that the particle only introduces a small perturbation of the
resonant field3. In any case, both numerical and experimental pictures show the field
enhancement inside the slot between the two cavities.
Figure 2 supplementary section 1| Field distributions of the resonant mode
with the field enhancement inside the slot. a, Scanning near-field optical
microscopy of the resonant mode of the fabricated structure. b, 3D FDTD calculation
in water of the resonant mode electric field intensity distribution. c, 3D FDTD
calculation in water of the resonant mode electric field intensity distribution with a 1
µm diameter polystyrene particle above the bottom cavity. The particle position is
shown by the dashed circle.
To get insights into the perturbation of the particle onto the coupled cavity, we simulated the
transmittance spectra by 3D FDTD in water for different particle positions as well as for
different number of particles. We display on Fig. 3 S1 a and b the numerical spectra, the black
ones being the references obtained without any particle. The schematics depict the central
positions of the particles above the coupled cavity. A redshift of the resonance which mainly
depends on the number of particles rather than on their relative position is observed. As a
result, increasing the number of trapped particles lead to a significant change in the
transmittance of the coupled cavity whereas fluctuations of the trapped particle position above
the coupled cavity only induces fluctuations of the transmittance.
Figure 3 section 1 supplementary information| 3D FDTD transmittance spectra
in water for different positions of trapped particles. a, Transmittance spectra of
the coupled cavity in water with a single particle at different positions above the
coupled cavity. The particle central position is pointed on the schematic. The black
spectrum is obtained without particle and is the reference. The colours of the other
spectra are related to the corresponding particle position indicated by a dot with the
same colour on the schematic. b, Same as a. but for two particles arranged
differently on the coupled cavity.
From the 3D FDTD calculation of the resonant mode in water used for trapping and sensing,
we also provide here the corresponding distribution of the gradient forces. The electric field
intensity distribution is reminded in Fig. 4 S1 a. A closer view to this electric field distribution
in the centre of the coupled cavities is superimposed to the corresponding gradient forces
distribution (Fig. 4 S1 b). Each antinode of the electric field clearly corresponds to a potential
trapping site.
Figure 4 supplementary section 1| FDTD calculations on laterally coupled
cavity and gradient field distribution. a, 3D FDTD calculation in water of the
electric field intensity distribution of the resonant mode. b, Zoom on field distribution
inside the dashed box shown in a, and superimposed to the gradient forces
distribution (black arrows).
Supplementary section 2| Longitudinally coupled cavity for particles
moving.
As shown on Fig. 1 S2 a, we measured the transmittance spectra of longitudinally coupled
cavity in air and in the colloidal solution. The coupled structure exhibits two resonances
whether in air or in the particles solution. The experimental results properly agree with the
numerical transmittance spectra on Fig. 1 S2 b obtained by 3D FDTD.
Figure 1 supplementary section 2| Spectra of the longitudinally coupled
cavities. a, Experimental spectra obtained in air (blue) and in the colloidal solution
(black). b, Three dimensional FDTD simulations of the corresponding transmittance
spectra in air (blue) and in the colloidal solution (black).
The near-field observations of the two resonant modes were then made by SNOM to check
the slight detuning between the cavities. The SNOM pictures are presented in Fig. 2 S2. The
3D calculations made in water for 2nm-detuned cavities are shown in Fig. 3 S2 a and b. As
visible on the SNOM measurements as well on 3D FDTD calculations, the electric field of the
resonant modes is non-equally distributed between the two cavities. The main field
localisation is achieved in the cavity on the left at the shorter resonance wavelength while it is
localised on the right for the other resonance.
Figure 2 supplementary section 2| SNOM observations of the detuned cavities.
a, Experimental field distribution at the shortest resonance wavelength b,
Experimental field distribution at the longest resonance wavelength.
In Fig. 3 S2 c. we superimposed the gradient forces distribution (black arrows) to an enlarged
view of the electric field distribution inside the cavity. Since the field distribution is the same
for the two cavities, we only provide one calculation of the forces distribution.
Figure 3 supplementary section 2| FDTD calculations on longitudinally coupled
cavity and gradient field distribution. a, and b, 3D FDTD calculations in water of
the electric field intensity distribution of the resonant modes at the shorter and longer
resonance wavelengths respectively. c, Zoom on the centre of the cavities shown in
the dashed boxes shown in a, and b, and superimposed to the corresponding
gradient forces distribution (black arrows).
Supplementary section 3| Three coupled cavity for dimer orientation
control.
The transmittance spectra of three coupled cavity in air and in the colloidal solution are shown
on Fig. 1 S3 a. The coupled structure exhibits three resonances whether in air or in the
particles solution. The experimental results properly agree with the numerical transmittance
spectra on Fig. 1 S3 b obtained by 3D FDTD. Only the two resonances at the longer
wavelengths are used for micromanipulation of the dimer shown in the main text.
Figure 1 supplementary section 3| Spectra of the three coupled cavity. a,
Experimental spectra obtained in air (blue) and in the colloidal solution (black). b,
Three dimensional FDTD simulations of the corresponding transmittance spectra in
air (blue) and in the colloidal solution (black).
The near-field observations of the three resonant modes were made by SNOM to check the
the proper coupling between the cavities and also to identify the enlightened cavities as a
function of the resonance wavelength. The SNOM pictures are presented in Fig. 2 S3 a, b and
c. Since the experimental field maps are equally distributed between the three cavities
according to the symmetry axis of the coupled structure, this confirms that they are properly
coupled. From shorter to longer wavelengths, it also evidences that the three resonances
switch on respectively all the cavities together (Fig. 2 S3 a), the two external ones (Fig. 2 S3
b) and the central one only (Fig. 2 S3 c).
Figure 2 supplementary section 3| SNOM observations of the three coupled
cavities. a, Experimental field distribution at the shortest resonance wavelength (1)
b, at central wavelength (2) and c, at the longest wavelength (3).
This properly agrees with 3D FDTD calculations shown in Fig. 3 S3 corresponding to the
modes of Fig. 2 S3 b and c used for the trapping experiments. For these two modes (2 and
3), we superimposed in Fig. 3 S3 b and d, the corresponding gradient forces distribution at
the centre of the three cavities. From this representation, it is clear that the two external
cavities consist in two dissociated trapping sites with equal probability at 2 while the central
cavity is the sole trapping site at 3.
Figure 3 supplementary section 3| FDTD calculations on three laterally coupled
cavity and gradient field distribution. a, and c, 3D FDTD calculations in water of
the electric field intensity distribution of the resonant modes at the resonance
wavelengths 2 and 3 respectively. b, and d, Zoom on the centre of the cavities
showing the field distribution in the dashed boxes shown in a, and c, and
superimposed to the corresponding gradient forces distribution (black arrows).
References:
1.
Lalouat, L. et al. Subwavelength imaging of light confinement in high Q/small V
photonic crystal nanocavity. Appl. Phys. Lett. 92, 111111 (2008).
2.
Lalouat, L. et al. Near field interactions between a subwavelength tip and a
small volume photonic crystal nanocavity. Phys. Rev. B 76, 041102 (2007).
3.
Cluzel, B. et al. A near field actuated optical nanocavity. Opt. Express 16, 279–
86 (2008).