The diffraction-limited resolution of light focused by a lens was derived in 1873 by Ernst Abbe. Later in 1952, a method to reach sub-diffraction light spots was proposed by modulating the wavefront of the focused beam. In a related development, super-oscillating functions, that is, band-limited functions that locally oscillate faster than their highest Fourier component, were introduced and experimentally applied for super-resolution microscopy. Up till now, only simple Gaussian-like sub-diffraction spots were used. Here we show that the amplitude and phase profile of these sub-diffraction spots can be arbitrarily controlled. In particular, we utilize Hermite–Gauss, Laguerre–Gauss and Airy functions to structure super-oscillating beams with sub-diffraction lobes. These structured beams are then used for high-resolution trapping and manipulation of nanometer-sized particles. The trapping potential provides unprecedented localization accuracy and stiffness, significantly exceeding those provided by standard diffraction-limited beams.
Trapping and manipulation of particles using laser beams has become an important tool in diverse fields of research. In recent years, particular interest is given to the problem of conveying optically trapped particles over extended distances either down or upstream the direction of the photons momentum flow. Here, we propose and demonstrate experimentally an optical analogue of the famous Archimedes' screw where the rotation of a helical-intensity beam is transferred to the axial motion of optically-trapped micro-meter scale airborne carbon based particles. With this optical screw, particles were easily conveyed with controlled velocity and direction, upstream or downstream the optical flow, over a distance of half a centimeter. Our results offer a very simple optical conveyor that could be adapted to a wide range of optical trapping scenarios.
Two colloidal particles, driven around an optical vortex trap, have been recently shown to pair due to an interplay between hydrodynamic interactions and the curved path they are forced to follow. We demonstrate here, that this pairing interaction can be tuned experimentally, and study its effect on the collective excitations of many particles driven around such an optical trap. We find that even though the system is overdamped, hydrodynamic interactions due to driving give rise to non-decaying excitations with characteristic dispersion relations. The collective excitations of the colloidal ring reflect fluctuations of particle pairs rather than those of single particles.
We propose a new method to image through dynamically changing turbid media based on the scanning of non-diffractive laser beams. We use computer-generated holograms to create Airy beams and compare quantitatively the characteristics of their propagation in clear and turbid media. Imaging contrast is achieved by relative reflection of the scanned beams from the imaged surface. We implement our method to demonstrate experimentally our ability to image a chromium surface on a glass slide through 270 μm of highly scattering milk/water mixtures with a resolution of several microns.
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...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2025 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.