Particle manipulation beyond the diffraction limit using structured super-oscillating light beams

• Published in: Light, science & applications Vol. 6; no. 9; p. e17050
• Main Authors: Singh, Brijesh K, Nagar, Harel, Roichman, Yael, Arie, Ady
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 08.09.2017; Springer Nature B.V; Nature Publishing Group
• Subjects: 639/624/1107/1110; 639/624/400/1103; Applied and Technical Physics; Atomic; Classical and Continuum Physics; Diffraction; Lasers; Localization; Molecular; Nanoparticles; Optical and Plasma Physics; Optical Devices; Optics; Original; original-article; Photonics; Physics; Physics and Astronomy; Trapping; optical tweezers; optical vortex; beam shaping; super-oscillating beams
• ISSN: 2047-7538; 2095-5545; 2047-7538
• DOI: 10.1038/lsa.2017.50

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. Optical trapping: structuring super-oscillating beams Optical trapping with enhanced spatial accuracy and stiffness is possible using super-oscillating light beams that have been structured. Scientists from Tel-Aviv University in Israel and the Central University of Rajasthan in India sent a laser beam to a spatial light modulator (SLM) whose phase could be programmed and then focused the beam using a high-numerical-aperture microscope objective. By applying suitable phase profiles to the SLM, they were able to generate super-oscillating beams with Laguerre-Gauss, Hermite-Gauss and Airy profiles that had features that were smaller than half the wavelength of the light used — the first time that subdiffraction structures have been produced in non-Gaussian beams. By performing optical trapping with these structured, super-oscillating beams, the team was able to manipulate polystyrene nanoparticles with enhanced precision and force than when conventional, diffraction-limited Gaussian beams were used.