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Plasmonic optical tweezers

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Harold Moreno

on 12 June 2013

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Transcript of Plasmonic optical tweezers

Josep Ingla and Harold Moreno
2013 Plasmon optical tweezers Sphere of radius R SPP sustained at a flat metal-dielectric interface. Cannot be coupled directly to propagating light Surface plasmon polaritons (SPP) vs. localized surface plasmons (LSP) The shift arises from the illumination asymmetry. Parallel trapping mechanism The subwavelength optical traps were produced near the surface of arrays of gold nanoparticles fabricated by high resolution electron beam lithography on a glass substrate, was made use of nanomolecules formed by gold nanodots arranged in tightly space pairs. Such geometry provides excellent control over the critical feature and the frequencies of the localized plasmon resonances, which can be exited by light of normal incidence. To demonstrate the action of nanometric optical tweezers, solid polystyrene
bead were trapped and nanomanipulated by a focused laser beam at
controlled focal distances from the surfaces of the nanoestructured
substrate, submerged into an immersion oil. Experimental Parameters Limitations in conventional optical tweezers Nanometric optical tweezers Much higher control of plasmonics fields can be achieved through an alternative technique that exploit the strong electromagnetic coupling between adjacent plasmonic nanoestructures, in these interesting geometry is: Subwavelength trapping with plasmonic antennas Gap antennas consist of two identical metallic particles separaed by a nanoscale dielectric gap. When the incident field is linearly polirezed along the vector connecting the particles, capacitive effects lead to a confined and intense light spot within the gap region. Sphere of radius 0.8 R Dependence of the restoring force with the radius. Diffraction prevents confinement beyond the diffraction limit How can we trap beyond the diffraction limit? Plasmons propagate light beyond the diffraction limit in the surface of a metal Beads diameters: 6 um, 1 um, 200 nm
oil refractive index: n=1.5 The studied structures were placed on a motorized x-y translation stage with
a position resolution of 20 nm. How can we measure this trapping potential? Photonic force microscope Area: 0.4 mm X 0.4 mm The data described were obtained on six samples with the same pair separation s=200 nm, lattice constant c=500 nm and height h=90 nm, the nanodots diameters changed Force done by the plasmons to a 4.5 um nanoparticle at 500 nm of the surface Other physical phenomena taking part Heat dissipation Migration from the center and self-assembly of the particles into an hcp array. Thermophoresis effect Linear array configuration Self-induced back-action (SIBA) trapping Migration from the center LSP Can be coupled directly to propagating light and only exist at a finite frequency range. The fact that LSP are located on the surface of a metallic nanoparticle or nanovoid allows us to control the traps one by one. Patterned metal The force at maximum coupling efficiency is 40 times stronger than the obtained without excitation Less metal surface implies less thermal convection. 200 nm Focus of the laser implies high power density Bibliography M. L. Juan, M. Righini, R. Quidant; Nature Photonics 5, 349-356 (2011)
G. Volpe, R. Quidant, G. Badenes, D. Petrov; Physical Review Letters 96, 238101 (4) (2006)
V. Garcés-Chávez, R. Quidant, P. J. Reece, G. Badenes, L. Torner, K. Dholakia; Physical Review B 73, 085417 (5) (2006)
M. Righini, A. S. Zelenina, C. Girard, R. Quidant; Nature Physics 3, 477-480 (2007)
A. N. Grigorenko, N. W. Roberts, M. R. Dickinson, Y. Zhang; Nature Photonics 2, 365-370 (2008)
M. L. Juan, R. Gordon, Y. Pang, F.Eftekhari, R. Quindant; Nature physics 5, 915-919 (2009) Thank you for your attention In the experiments, the symmetric
resonance of the double-pillar nanomolecule was excited
by the infrared laser light, lambda=1064 nm
An generate the strong electromagnetic fields required for operation of the nanometric tweezers This figure shows cross-section of the electromagnetic field intensity of near-fields exited by the 1064 nm light wavefront and calculated using femlab software. The calculations suggest that the double pillar nanomolecules could yield a near field trap with a typical size of 100 nm and offer an amplification of the trapping force by almost two order of magnitude near the nanoestructure surface The previous figures show that a 200 nm bead can be pinned in a near-field sub wavelength trap above any illuminated nanodot pair in the array and can be moved from one double-pillar nanomolecule to another one simply by moving the beam along the array . It implies that a lattice of nanodots provides a rigid set of sub wavelenght near field traps in which the particle can be positioned with very high accuracy Future outlook and applications SP nano-tweezers in future integrated analytical devices From nano traps to nano tweezers Quantum information Continuous-wave of 1 W, 1064 nm neodymium-doped diode pump solid-state laser
Beam diameter: 5 mm
NA: 1.3 In this case is combined optical and nanomagnetic force fields,
is studied the possibility of creating a single-atom nanotrap at the
extremity of a sharply elongated optical near-field tip. Conclusions Optical tweezers are a powerful device to manipulate bio-systems at the micrometer scale.
Optical limitations prevent us to trap objects smaller than micrometers.
Plasmon optical tweezers can trap nanometer sized dielectric spheres in the interface between a metal and a dielectric.
The use of plasmonic antennas provide us 3D traps as fine as our precision to build a nanostructure with a small gap.
The reported techniques have the inconvenience that the intensity required can cause damage of our samples. To avoid this we can use SIBA effect that doesn't require much intensity. Sometimes the power density required to trap a biological specimen exceeds its damage threshold. To avoid this, a different trapping method has been demonstrated: Sample mounted upside-down 100 nm particle Resonance in the cavity Forces taking part 100 nm 50 nm Grad. F Comp. MST F Both We can observe longer trapping times for higher incident powers. Arrhenius law Comprehensive force is much higher than the gradient, this enhances the trapping without extra energy. These variations
correspond to a
respective increase
of the stiffness from
0.0001pN/nm to
0,013pN/nm Stiffness of the optical trap: 1.1 pN/um
3 mW z=10 um
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