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Optical encryption strategies utilizing fully coherent light have been widely explored but often face challenges such as speckle noise and beam instabilities. In this work, we introduce a novel protocol for multi-channel optical information encoding and encryption using vectorial spatial coherence engineering of a partially coherent light beam. By characterizing the beam's spatial coherence structure with a 2 × 2 coherence matrix, we demonstrate independent control over the three components of the coherence Stokes vector. This allows for three-channel optical information encoding and encryption, with applications in color image representation. Unlike existing methods based on fully coherent light modulations, our approach utilizes a two-point dependent coherence Stokes vector, proving resilient to random noise in experimental scenarios. Our findings provide a robust foundation for higher-dimensional optical encoding and encryption, addressing limitations associated with partially coherent light in complex environments. [ABSTRACT FROM AUTHOR]

A coherence-orbital angular momentum (COAM) matrix describes the second-order spatial correlations among the pairs of the OAM states in a light beam at two radial positions. It provides a detailed information regarding the azimuthal features of the light beam itself or of the objects interacting with it. In this Letter, we reveal a close relationship existing between the COAM matrix's elements of a partially coherent light beam and the angular gratings that it passes through. It is demonstrated both in theory and in experiment that all the parameters of the angular gratings can be identified by measuring the COAM matrix elements. While the off-diagonal elements possess information about the angular shifts and the rotation speed of the angular grating, the diagonal elements account for the energy distribution among the OAM modes. The experimental results agree reasonably well with the theoretical analysis. One practically significant capability is that our technique offers the determination of angular shifts of azimuthally symmetric objects and/or their rotational speed, by means of a single-pixel detector. [ABSTRACT FROM AUTHOR]

We propose a compact method to experimentally synthesize a class of vector beam arrays with periodic higher-order Poincaré sphere (HOPS) polarization states by engineering the spatial coherence structure of a partially coherent light source. We demonstrate that the spatial coherence structure and polarization state of the partially coherent source can be simultaneously controlled using a phase-only spatial light modulator and a common-path interferometric arrangement with the aid of a complex-random-mode representation method. We show experimentally that the polarization state of a single HOPS beam in the source plane can be mapped into a beam array generated in the far field, and the degree of polarization of the beam array can be conveniently controlled with spatial coherence engineering. Our method provides an alternative way to synthesize beam arrays with structured coherence and polarization properties. [ABSTRACT FROM AUTHOR]

We examine the effect of spatial coherence on the image quality of a classic 4f imaging system when its Fourier plane is partially blocked by an opaque obstacle. We find that although reducing the degree of spatial coherence of the source results in the improved image quality, the concurrent distortions in the image plane are inevitable. Employing a suitable decomposition of a partially coherent light source into a set of coherent pseudo-modes with a multitude of linear phase shifts, we demonstrate that the distortions are primarily induced by the modes whose maxima are located at the obstacle edges. We show that by tailoring spatial coherence of the source we can enable all the coherent modes to circumnavigate the obstacle, ensuring the same image quality as if the obstacle were absent from the Fourier plane. We expect our findings to be instrumental in high-contrast optical microscopy with coherence structured light. [ABSTRACT FROM AUTHOR]

We derive theoretically and verify experimentally a concise general expression for the normalized intensity correlations (IC) of partially coherent light in a weak atmospheric turbulence in the fast detector measurement regime. The derived relation reveals that the medium turbulence acts, in general, as an additional noise source enhancing the IC of partially coherent beams. The maximum of the beam IC is, in general, enhanced, causing the fields to exhibit super-Gaussian statistics. On the other hand, the relation indicates that turbulence-induced noise is negligible for sufficiently low coherence light, which reveals the condition for the turbulence-free correlation imaging. [ABSTRACT FROM AUTHOR]

We introduce a new kind of partially coherent beam with nonconventional correlation function named rectangular Laguerre-Gaussian-correlated Schell-model (LGCSM) beam, whose degree of coherence is of rectangular symmetry, and analyze its propagation properties. We find that the rectangular LGCSM beam exhibits self-splitting properties on propagation in free space, i.e., the initial single beam spot evolves into ( m + 1) × ( n + 1) beam spots on propagation with m and n being the beam orders, which are totally different from that of a circular or elliptical LGCSM beam. The self-splitting properties of a rectangular LGCSM beam are also different from other self-splitting beam whose initial single beam spot only splits into two or four beam spots on propagation in free space. We also find that a focused rectangular LGCSM beam exhibits splitting and combining properties on propagation. Furthermore, we carry out experimental generation of a rectangular LGCSM beam and verify the splitting and combining properties of such beam focused by a thin lens. The rectangular LGCSM beam will be useful for manipulating multiple particles or attacking multiple targets simultaneously. [ABSTRACT FROM AUTHOR]

With the help of a tensor method, we derive an explicit expression for the on-axis scintillation index of a circular partially coherent dark hollow (DH) beam in weakly turbulent atmosphere. The derived formula can be applied to study the scintillation properties of a partially coherent Gaussian beam and a partially coherent flat-topped (FT) beam. The effect of spatial coherence on the scintillation properties of DH beam, FT beam and Gaussian beam is studied numerically and comparatively. Our results show that the advantage of a DH beam over a FT beam and a Gaussian beam for reducing turbulence-induced scintillation increases particularly at long propagation distances with the decrease of spatial coherence or the increase of the atmospheric turbulence, which will be useful for long-distance free-space optical communications. [ABSTRACT FROM AUTHOR]

• Spatial coherence structure of a partially coherent light beam can be used as a novel tool for the manipulation of optical radiation force. • The symmetry of trapping area can be modulated by the symmetry of the spatial coherence structure of the incident light beam. • Two types of Rayleigh dielectric particles of different refractive indices can be trapped simultaneously by a focused rotational elliptical Laguerre–Gaussian correlated Schell-model beam. • The effects of beam order and spatial coherence widths on the radiation forces are analyzed in detail. We analyze the optical radiation forces, produced by a focused rotational elliptical Laguerre–Gaussian correlated Schell-model (ELGSM) beam, on the dielectric particles of different refractive indices in the Rayleigh scattering regime. It is found that through a judicious modulation of the initial spatial coherence width and the beam order of the correlation function of the rotational ELGSM beam, the particles with higher refractive index (compared with the ambient) can be trapped along an elliptical ring centered at the focus, the particles with lower refractive index, at the same time, will be trapped at the focal point. Our results also show that the trapping area/range can be modulated by structuring the correlation function of the beam. By comparing the gradient, scattering, Brownian, and gravity forces acting on the particles, the trapping stability is analyzed. Our results indicate that the coherence structure engineering can be used as an alternative approach to modulate the symmetry of the optical trapping area. [ABSTRACT FROM AUTHOR]

Abstract: We report experimental generation of a polychromatic partially coherent dark hollow beam (DHB) by coupling a polychromatic beam emitted from a light-emitting diode into a multimode fiber. The normalized spectrum of the generated partially coherent DHB is similar to that of the incident beam, while spectral shift exists. From the results of the double-slit interference experiment, we demonstrate that the multimode fiber increases the coherence of the output beam. Our method provides a convenient way for producing a polychromatic partially coherent dark hollow beam. [Copyright &y& Elsevier]

Optical coherence is a fundamental characteristic of light that plays a significant role in understanding interference, propagation, light–matter interaction, and other fundamental aspects of classical and quantum wave fields. The study of optical coherence has led to a wide range of applications, including optical coherence tomography, ghost imaging, and free-space optical communications. In recent years, the complex spatial structure of optical coherence embedded in partially coherent light beams has garnered increasing attention due to the novel physical effects it induces, such as self-shaping, self-focusing, and self-splitting of beams in free space. Partially coherent light beams with non-classical spatial coherence structures have found use in many innovative applications, including overcoming the classical Rayleigh diffraction limit in optical imaging, reducing the side effects of atmospheric turbulence in free-space optical communications, coherence-based optical encryption, and robust optical signal transmission. In this article, we present a systematic review of the manipulation and measurement of the spatial coherence structure of optical beams, their propagation and light–matter interaction, as well as the applications of partially coherent light beams with structured optical coherence. We begin with the representation of the cross-spectral density function for a partially coherent light beam using Gori's nonnegative definite condition and Wolf's coherent-mode decomposition theory. We then discuss in detail two different strategies for experimentally manipulating the spatial coherence structure, one based on the generalized van Cittert–Zernike theorem and the other on the coherent-mode decomposition theory. Next, we provide an overview of recent progress in measuring the complex spatial coherence structure of partially coherent light beams using methods based on self-referencing holography, generalized Hanbury Brown and Twiss experiment, and incoherent modal decomposition. We study the novel physical properties of partially coherent light beams with non-conventional spatial coherence structures during their propagation in free space and through a highly focused system, as well as their interaction with atmospheric turbulence. We also discuss the effect of structured optical coherence in reducing the negative effects of atmospheric turbulence. Finally, we present the applications of spatial coherence structure engineering in optical imaging, optical encryption, robust information transmission through complex media, particle trapping, refractive index measurement, beam shaping, and ultrahigh precision angular velocity measurement. Optical coherence structure not only provides a new degree of freedom for light manipulation but also offers an effective tool for novel light applications. [ABSTRACT FROM AUTHOR]