Extreme axial optical force in a standing wave achieved by optimized object shape

Trojek, Jan; Karásek, Vítězslav; Zemánek, Pavel

doi:10.1364/oe.17.010472

Cited by 11 publications

(8 citation statements)

References 51 publications

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“…Other useful e↵ects have been demonstrated, including anti-reflection coated beads for applying nN trapping forces [7] and optical wings that exhibit stable optical lift [8,9]. More generally, shaping of colloidal particles allows control of their mechanical interaction with light at a fundamental level [10][11][12]; the recent proliferation of 2-photon polymerisation systems opens up new possibilities for designing novel optical tweezers experiments.…”

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confidence: 99%

Shape-induced force fields in optical trapping

et al. 2014

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Advances in optical tweezers, coupled with the proliferation of 2-photon polymerisation systems, mean that it is now becoming routine to fabricate and trap non-spherical particles. The shaping of both light beams and particles allows fine control over the flow of momentum from the optical to mechanical regimes. However, understanding and predicting the behaviour of such systems is highly complex in comparison with the traditional optically trapped microsphere. In this paper we present a conceptually new and simple approach, based on the nature of the optical force density. We illustrate the method through the design and fabrication of a shaped particle capable of acting as a passive force clamp; we demonstrate its use as an optically trapped probe for imaging surface topography. Further applications of the design rules highlighted here may lead to new sensors for probing bio-molecule mechanics, as well as to the development of optically actuated micro-machines.It is well known that the high intensity gradients generated in a tightly focused laser beam can be used to trap and manipulate micron-sized particles [1]. An optically trapped sphere is an elegant example of a microscopic harmonic oscillator, capable of measuring fN-scale forces, which has proved invaluable for the study of molecular motors and single biopolymer mechanics [2]. However, there are other desirable features of a force field that can only be introduced by modifying the particle shape or dielectric structure beyond that of a simple homogeneous sphere [3,4]. For example, optical torques can be applied to a particle whose symmetry has been lowered either by shape modification With increasing complexity of shape, the problem of predicting, and optimising, the 2 force profile of the trapped particle becomes ever more challenging. Although specialised software packages are available to compute the optical forces [13], their use is not routine.In this paper, therefore, we address this problem and describe a straightforward method for predicting the optical forces acting on extended dielectric particles of general shape. We support the description with rigorous 3-dimensional T-matrix calculations. To illustrate the approach, we describe the design and fabrication of a passive force clamp based on a tapered cylinder and capable of applying a constant force over displacements of several microns. We demonstrate its use in an optically-controlled scanning probe microscope for ultra-low force imaging. Potential future applications of this device may include the imaging of sensitive biological membranes. Results Background theory

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confidence: 99%

Shape-induced force fields in optical trapping

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“…It has been shown theoretically that the strong modulation of the axial intensity due to interference can increase the axial trap stiffness of submicrometer particles in a standing wave optical trap by at least 2 orders of magnitude over that in a single beam optical trap. 8,9 Therefore, the axial fluctuations of the Ag nanoparticles over the Au nanoplates would be (at least) an order of magnitude smaller than over the transparent glass since κ −1 ∝ σ 2 . 11,31 Indeed, as shown in Figure 6, optical binding depends nontrivially on the axial configuration.…”

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Enhancing Nanoparticle Electrodynamics with Gold Nanoplate Mirrors

et al. 2014

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Mirrors and optical cavities can modify and enhance matter-radiation interactions. Here we report that chemically synthesized Au nanoplates can serve as micrometer-size mirrors that enhance electrodynamic interactions. Because of their plasmonic properties, the Au nanoplates enhance the brightness of scattered light from Ag nanoparticles near the nanoplate surface in dark-field microscopy. More importantly, enhanced optical trapping and optical binding of Ag nanoparticles are demonstrated in interferometric optical traps created from a single laser beam and its reflection from individual Au nanoplates. The enhancement of the interparticle force constant is ≈20-fold more than expected from the increased intensity due to standing wave interference. We show that the additional stability for optical binding arises from the restricted axial thermal motion of the nanoparticles that couples to and reduces the fluctuations in the lateral plane. This new mechanism greatly advances the photonic synthesis of ultrastable nanoparticle arrays and investigation of their properties.

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“…This approach has been used by Trojek et al to study extreme axial optical forces in a standing wave achieved by optimizing the object shape [214]. Tynnelä et al studied single-particle negative polarization at intermediate scattering angles [215].…”

Section: Other Light Scattering Methodsmentioning

confidence: 99%