Enhancing the Strength of an Optical Trap by Truncation

Rodrigues, Vanessa R. M.; Mondal, Angana; Dharmadhikari, J. A.; Panigrahi, Swapnesh; Mathur, D.; Dharmadhikari, A. K.

doi:10.1371/journal.pone.0061310

Cited by 3 publications

(3 citation statements)

References 27 publications

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“…Finally, we take into account that the intensity of the laser beam changes also the stiffness of the laser trap, η. Assuming again a linear relationship [44], i.e. η ∝ I, we can write…”

Section: Strategy Of Controlmentioning

confidence: 99%

Delayed feedback control of active particles: a controlled journey towards the destination

Khadem

Klapp

2019

Phys. Chem. Chem. Phys.

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We explore theoretically the navigation of an active particle based on delayed feedback control. The delayed feedback enters in our expression for the particle orientation which, for an active particle, determines (up to noise) the direction of motion in the next time step. Here we estimate the orientation by comparing the delayed position of the particle with the actual one. This method does not require any real-time monitoring of the particle orientation and may thus be relevant also for controlling sub-micron sized particles, where the imaging process is not easily feasible. We apply the delayed feedback strategy to two experimentally relevant situations, namely, optical trapping and photon nudging. To investigate the performance of our strategy, we calculate the mean arrival time analytically (exploiting a small-delay approximation) and by simulations.jebreiilkhadem@itp.tu-berlin.de arXiv:1811.06849v4 [cond-mat.stat-mech]

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“…Finally, we take into account that the intensity of the laser beam changes also the stiffness of the laser trap, η. Assuming again a linear relationship [44], i.e. η ∝ I, we can write…”

Section: Strategy Of Controlmentioning

confidence: 99%

Delayed feedback control of active particles: a controlled journey towards the destination

Khadem

Klapp

2019

Phys. Chem. Chem. Phys.

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“…0.8, 40x) was conjugated onto a digital camera (Pixelfly USB, PCO) using a 30 mm focal length lens. This long working distance objective, which was selected for ease of measurement 27 , has been previously been demonstrated to create a 3D trap 28 with stiffness of around 0.03–0.04 pN/µm.…”

Section: Introductionmentioning

confidence: 99%

Structured Back Focal Plane Interferometry (SBFPI)

Upadhya

Zheng

et al. 2019

Sci Rep

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Back focal plane interferometry (BFPI) is one of the most straightforward and powerful methods for achieving sub-nanometer particle tracking precision at high speed (MHz). BFPI faces technical challenges that prohibit tunable expansion of linear detection range with minimal loss to sensitivity, while maintaining robustness against optical aberrations. In this paper, we devise a tunable BFPI combining a structured beam (conical wavefront) and structured detection (annular quadrant photodiode). This technique, which we termed Structured Back Focal Plane Interferometry (SBFPI), possesses three key novelties namely: extended tracking range, low loss in sensitivity, and resilience to spatial aberrations. Most importantly, the conical wavefront beam preserves the axial Gouy phase shift and lateral beam waist that can then be harnessed in a conventional BFPI system. Through a series of experimental results, we were able to tune detection sensitivity and detection range over the SBFPI parameter space. We also identified a figure of merit based on the experimental optimum that allows us to identify optimal SBPFI configurations that balance both range and sensitivity. In addition, we also studied the resilience of SBFPI against asymmetric spatial aberrations (astigmatism of up to 0.8 λ) along the lateral directions. The simplicity and elegance of SBFPI will accelerate its dissemination to many associated fields in optical detection, interferometry and force spectroscopy.

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“…Over the last 20 years SO beams were generated using different methods [7-9] and applied for super-resolution imaging [10,11].The effect of particle size, beam waist, and wavelength on the stiffness of optical trapping was studied theoretically for different scattering regimes [12][13][14]. Experimental verification of these predictions is challenging since neither beam size, wavelength, nor particle size can be changed continuously to provide a clean comparison [15][16][17][18]. Naturally, all previous measurements focused on diffraction-limited optical traps.…”

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confidence: 99%

Optical trapping below the diffraction limit with a tunable beam waist using super-oscillating beams

et al. 2019

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Super-oscillating beams can be used to create light spots whose size is below the diffraction limit with a side ring of high intensity adjacent to them. Optical traps made of the super-oscillating part of such beams exhibit superior localization of submicron beads compared to regular optical traps. Here we focus on the effect of the ratio of particle size to trap size on the localization and stiffness of optical traps made of super-oscillating beams. We find a non-monotonic dependence of trapping stiffness on the ratio of particle size to beam size. Optimal trapping is achieved when the particle is larger than the beam waist of the super-oscillating feature but small enough not to overlap with the side ring. PACS numbers:In the early 70s, Artur Ashkin showed that a weakly focused laser beam can draw small particles with high refractive index towards its center and move them in the direction of light propagation [1]. A major breakthrough in this field happened in 1986 when Ashkin demonstrated the single beam optical gradient force traps [2], known nowadays as optical tweezers. Since then, optical trapping application has become a powerful tool used in physics and biology. However, the size of an optical trap is limited by the smallest spot which collimated light can be focused to using an annular aperture, as discussed in 1873 by Ernst Abbe [3] and later by Lord Rayleigh [4]. The diffraction limit of light determining this minimal beam size is given by w = 0.38λ/NA, where w is the beam waist defined as the full width at half maximum of the beam, λ is the wavelength of the beam, and NA is the numerical aperture of the focusing lens. In 1952 G. Toraldo di Francia suggested theoretically that by phase modulations one can achieve optical features below the diffraction limit [5]. In the 90's the concept of super oscillation (SO) was first introduce by Michel Berry for bandlimited functions that locally oscillate faster than their highest Fourier component [6]. In optics, the SO phenomena was used to generate optical beams with features smaller than the diffraction limit. Over the last 20 years SO beams were generated using different methods [7-9] and applied for super-resolution imaging [10,11].The effect of particle size, beam waist, and wavelength on the stiffness of optical trapping was studied theoretically for different scattering regimes [12][13][14]. Experimental verification of these predictions is challenging since neither beam size, wavelength, nor particle size can be changed continuously to provide a clean comparison [15][16][17][18]. Naturally, all previous measurements focused on diffraction-limited optical traps. Previously, we observed that a significant enhancement of optical trapping strength and localization occurred when a 490 nm particle was trapped in the SO part of a SO beam [19]. Here we study this effect in more detail. We use the unique feature of SO beams, namely, the ability to change continuously the beam waist and to focus the beam to below the diffraction limit, to measure the effect of p...

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Enhancing the Strength of an Optical Trap by Truncation

Cited by 3 publications

References 27 publications

Delayed feedback control of active particles: a controlled journey towards the destination

Delayed feedback control of active particles: a controlled journey towards the destination

Structured Back Focal Plane Interferometry (SBFPI)

Optical trapping below the diffraction limit with a tunable beam waist using super-oscillating beams

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