Optical tweezers: theory and practice
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Optical tweezers: theory and practice Giuseppe Pesce1,a , Philip H. Jones2 , Onofrio M. Maragò3 , Giovanni Volpe4 1 Department of Physics, Università degli di Studi di Napoli “Federico II” Complesso Universitario Monte S.
Angelo, Via Cintia, 80126 Naples, Italy
2 Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT,
UK
3 CNR-IPCF, Istituto Processi Chimico-Fisici, V.le F. Stagno D’Alcontres 37, 98158 Messina, Italy 4 Department of Physics, University of Gothenburg, 41296 Gothenburg, Sweden
Received: 1 July 2020 / Accepted: 6 October 2020 © The Author(s) 2020
Abstract The possibility for the manipulation of many different samples using only the light from a laser beam opened the way to a variety of experiments. The technique, known as Optical Tweezers, is nowadays employed in a multitude of applications demonstrating its relevance. Since the pioneering work of Arthur Ashkin, where he used a single strongly focused laser beam, ever more complex experimental set-ups are required in order to perform novel and challenging experiments. Here we provide a comprehensive review of the theoretical background and experimental techniques. We start by giving an overview of the theory of optical forces: first, we consider optical forces in approximated regimes when the particles are much larger (ray optics) or much smaller (dipole approximation) than the light wavelength; then, we discuss the full electromagnetic theory of optical forces with a focus on T-matrix methods. Then, we describe the important aspect of Brownian motion in optical traps and its implementation in optical tweezers simulations. Finally, we provide a general description of typical experimental setups of optical tweezers and calibration techniques with particular emphasis on holographic optical tweezers.
1 Introduction The ability of light to exert a force on matter was recognised as early as 1619 by Kepler [1] who first described the deflection of comet tails by the rays of the sun. However, only the inclusion of light phenomena within Maxwell’s theory of electromagnetism in the late nineteenth century led to the prediction of radiation pressure along the direction of light propagation [2]. Early experiments to detect the mechanical effects of light were performed by Nichols and Hull [3] and Lebedev [4], who succeeded in detecting the radiation pressure acting on macroscopic objects using thermal light sources (electric or arc lamps) and a torsion balance. A few decades later, Beth [5] reported the first experimental observation of the torque on a macroscopic object resulting from interaction with light: he observed the deflection of a quartz wave plate suspended from a thin quartz fiber when circularly polarised light passed
We would like to dedicate this paper to the memory of Arthur Ashkin (1922–2020). a e-mail: [email protected] (corresponding author)
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Fig. 1 Typical objects that are trapped in optical manipulation ex
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