https://physicstoday.scitation.org/doi/pdf/10.1063/1.3047693

Introduction to the Theory of Coherence and Polarization of Light

Optical trapping describes the interaction between light and matter to manipulate micro-objects through momentum transfer. In the case of 3D trapping with a single beam, this is termed optical tweezers. Optical tweezers are a powerful and noninvasive tool for manipulating small objects, and have become indispensable in many fields, including physics, biology, soft condensed matter, among others. In the early days, optical trapping was typically accomplished with a single Gaussian beam. In recent years, we have witnessed rapid progress in the use of structured light beams with customized phase, amplitude, and polarization in optical trapping. Unusual beam properties, such as phase singularities on-axis and propagation invariant nature, have opened up novel capabilities to the study of micromanipulation in liquid, air, and vacuum. We summarize the recent advances in the field of optical trapping using structured light beams.

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Optical trapping with structured light: a review

Partially coherent beams with nonconventional correlation functions have displayed many extraordinary properties, such as self-focusing and self-splitting, which are totally different from those of partially coherent beams with conventional Gaussian correlated Schell-model functions and are useful in many applications, such as optical trapping, free-space optical communications, and material thermal processing. In this paper, we present a review of recent developments on generation and propagation of partially coherent beams with nonconventional correlation functions.

Generation and propagation of partially coherent beams with nonconventional correlation functions: a review [invited].

Partially coherent beam is preferred in many applications, such as free-space optical communications, remote sensing, active laser radar systems, etc., due to its resistance to the deleterious effects of atmospheric turbulence. In this paper, after presenting a historical overview on propagation of optical beams in turbulent atmosphere, we describe the basic theory for treating the propagation of optical beams in turbulent atmosphere and we mainly introduce recent theoretical and experimental developments on propagation of partially coherent beam in turbulent atmosphere. Recent progress on the interaction of a partially coherent beam with a semirough target in turbulent atmosphere and the corresponding inverse problem are also reviewed.

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Propagation of Partially Coherent Beam in Turbulent Atmosphere: a Review (Invited Review)

Cosine-Gaussian-correlated Schell-model sources whose degree of coherence (DOC) is of circular symmetry have been introduced just recently [Opt. Lett.38, 2578 (2013)]. In this Letter, we propose a model for a source whose DOC is the superposition of two 1D cosine-Gaussian-correlated Schell-model sources, i.e., possesses rectangular symmetry. The novel model sources and beams they generate are termed rectangular cosine-Gaussian Schell-model (RCGSM). The RCGSM beam exhibits unique features on propagation, e.g., its intensity in the far field (or in the focal plane) displays a four-beamlet array profile, being qualitatively different from the ring-shaped profile of the CGSM beam whose DOC is of circular symmetry. Furthermore, we have carried out experimental generation of the proposed beam and measured its focusing properties. Our experimental results are consistent with the theoretical predictions.

Experimental generation of cosine-Gaussian-correlated Schell-model beams with rectangular symmetry

We introduce a general optical system for synthesis of partially coherent vector beams with a variety of correlation functions. In particular we employ it for generation of the family of beams, termed the specially correlated radially polarized (SCRP) beams and examine their free-space propagation both theoretically and experimentally. Our results clearly show that a SCRP beam exhibits unique features on propagation in comparison with those of beams with conventional correlation functions. The technique for modulation of the correlation functions and, hence, the coherence state of a SCRP beam in the source plane leads to efficient control of its intensity distribution and its degree of polarization on propagation, which is of importance in particle trapping and material thermal processing applications.

Generation and propagation of a partially coherent vector beam with special correlation functions

Partially coherent beams with a prescribed phase, state of polarization, and degree of coherence display many extraordinary propagation properties and are preferred in many applications, such as particle trapping, free-space optical communications, remote sensing, optical imaging, material thermal processing, image transformation, and optical encryption. In this review, we begin with describing conventional Gaussian Schell-model beams and partially coherent beams with prescribed phases, states of polarization, and degrees of coherence. Then we introduce theoretical models for various partially coherent beams and the methods for generating them. Finally, a brief summary is presented.

Generation of Partially Coherent Beams

We carry out experimental measurement of the scintillation index of a partially coherent beam-carrying vortex phase (i.e., Gaussian–Schell model vortex beam) propagating through thermally induced turbulence. It is demonstrated that a Gaussian–Schell model vortex beam has appreciably smaller scintillation than a Gaussian–Schell model beam, which will be useful in free-space optical communication.

Experimental demonstration of vortex phase-induced reduction in scintillation of a partially coherent beam.

Radially polarized (RP) beam with controllable spatial coherence (i.e., partially coherent RP beam) was generated in experiment recently [Appl. Phys. Lett. 100, 051108 (2012)]. In this letter, we report experimental study of the scintillation index of a partially coherent RP beam propagating through thermally induced turbulence. Our results show that a partially coherent RP beam has advantage over a linearly polarized partially coherent beam for reducing turbulence-induced scintillation, which will be useful in free-space optical communications, remote sensing and laser radar systems.

Experimental study of the scintillation index of a radially polarized beam with controllable spatial coherence

A new kind of partially coherent beam with non-conventional correlation function named elliptical Laguerre-Gaussian correlated Schell-model (LGCSM) beam is introduced. Analytical propagation formula for an elliptical LGCSM beam passing through a stigmatic ABCD optical system is derived. The elliptical LGCSM beam exhibits unique features on propagation, e.g., its intensity in the far field (or in the focal plane) displays an elliptical ring-shaped beam profile, being qualitatively different from the circular ring-shaped beam profile of the circular LGCSM beam. Furthermore, we carry out experimental generation of an elliptical LGCSM beam with controllable ellipticity, and measure its focusing properties. Our experimental results are consistent with the theoretical predictions. The elliptical LGCSM beam will be useful in atomic optics.

Lin Liu

Papers

Generation and propagation of a partially coherent vector beam with special correlation functions

Generation of Partially Coherent Beams

Experimental demonstration of vortex phase-induced reduction in scintillation of a partially coherent beam.

Experimental study of the scintillation index of a radially polarized beam with controllable spatial coherence

Elliptical Laguerre-Gaussian correlated Schell-model beam.