Supplementary information
Optofluidic taming of a colloidal dimer with a silicon nanocavity
C. Pin,1,2,3 B. Cluzel,1,a) C. Renaut,1,2,3 D. Peyrade,3 E. Picard,2 E. Hadji,2 and F.
de Fornel1
1
Groupe d’Optique de Champ Proche - LRC CEA n°DSM-08-36, Laboratoire Interdisciplinaire Carnot de Bourgogne.
UMR CNRS n°6303- Université de Bourgogne, Dijon, France
2
Univ. Grenoble Alpes, INAC-SP2M-SINAPS, F-38000 Grenoble, France
CEA, INAC-SP2M-SINAPS, F-38000 Grenoble, France
3
Univ. Grenoble Alpes, CNRS, CEA-Leti Minatec, LTM, F-38054 Grenoble Cedex, France
Additional data concerning single particle trapping experiments are presented here to understand the
selective trapping of the dimer smallest bead as it is reported in this paper. The same nanocavity as for
the dimer trapping was also used to trap 1 and 2 µm diameter single particles with the same laser source
input power (8 mW) and wavelength (1556 nm).
Figures S1 (a) and (b) show the recorded positions of the trapped single particles. Histograms of the
particles positions along the waveguide direction and along the orthogonal direction are also plotted to
visualize the trapped particles position distributions. Gaussian fits of these position distributions enable
to calculate the stiffness of the optical trap in both directions. It is found that, in the case of the 2 µm
particle, the trap stiffness along the waveguide axis (kx = 0.06 fN.nm-1) is an order of magnitude smaller
than in the case of the 1 µm particle (kx = 0.9 fN.nm-1). This result can be explained by the complex
field distribution of the cavity resonant mode1: the 1 µm bead is mainly trapped by one single intensity
peak of the resonant mode at a time (similarly to previously reported 200 nm bead trapping
a)
Electronic mail : benoit.cluzel@u-bourgogne.fr
1
experiments2), whereas both the 2 highest intensity peaks of the resonant mode compete at the same
time to trap the 2 µm bead, which leads to a much unstable and hence weaker optical trap. Therefore, the
optical forces applying on a 1 µm bead are stronger than the optical forces applying on a 2 µm bead. In
the experiments reported in this paper, the 1 µm bead of the heterogeneous dimer is thus preferentially
trapped on the nanocavity.
(a)
(b)
FIG. S1. Recorded positions of (a) 1 µm and (b) 2 µm beads trapped above the nanocavity. Histograms of positions along
orthogonal directions are plotted and the position distributions are approximated with Gaussian fits. Corresponding trap
stiffnesses are indicated on each histogram.
REFERENCES
1
L. Lalouat, B. Cluzel, F. de Fornel, P. Velha, P. Lalanne, D. Peyrade, E. Picard, T. Charvolin, and E.
Hadji, Applied Physics Letters 92, 111111 (2008).
2
S. Mandal, X. Serey, and D. Erickson, Nano Letters 10, 99 (2010).
2