This PDF file contains the front matter associated with SPIE Proceedings Volume 12901, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

A quarter century of progress in holographic optical trapping has yielded fundamental advances in the science of classical wave-matter interactions. These efforts have drawn attention to the connection between wavefront topology and wave-mediated forces, including the interrelated roles of orbital and spin angular momentum, and the interplay between conservative intensity-gradient forces and non-conservative phase-gradient forces. Holographically structured force landscapes can act as knots, micromachines and even tractor beams and have permeated application areas ranging from biomedical research to quantum computing. Lessons learned from holographic optical trapping recently have been applied to acoustic micromanipulation, with remarkable effect. Beyond an overall leap in the force scales that can be achieved with sound, advances in acoustic trapping are casting new light on the nature of wave-matter interactions, including the role of nonreciprocal wave-mediated interactions in creating novel states of organization.

In this computational study we examine the behaviour of mixed-refractive index colloidal clusters. The clusters consist of bonded collections of spherical nanospheres with different refractive indices. The behaviour of these clusters in optical traps varies depending on the numbers of particles involved and the overall symmetry of the cluster. The symmetry can be varied by changing the refractive indices. It has been shown that breaking the symmetry of a cluster by, for example, introducing a single high refractive index impurity can produce a pronounced impact on the dynamics of the cluster in an optical trap [Davie et al. Proc. SPIE 12649, 126490E (2023)]. In the present study we will explore the dynamics of mixed refractive index clusters counter propagating plane waves and in different types of optical trap. Optical forces are calculated using the discrete dipole approximation; dynamics are computed using Brownian dynamics, with hydrodynamic interactions in the low Reynolds number regime and particle separations are constrained using the SHAKE-HI algorithm.

Lateral optical forces (LOFs) exerted on metamaterials typically arise from broken mirror symmetry in the system. In previous studies, we have demonstrated that, in addition to asymmetric particle or motif pairs, a periodic array of isosceles triangle motifs with carefully chosen shape can also exert large LOFs under plane wave illumination. In this study, we further explore this phenomenon systematically with consideration of thickness of the triangle motif. Results demonstrate new insight on how LOFs relate to the shape of triangle motifs.

Skyrmions are topologically protected field configurations characterised by a topological index, the skyrmion number. Optical skyrmions are ideally suited to investigate topological structures due to the ease of generating arbitrary light fields, and the freedom from energy constraints encountered by, for example, magnetic skyrmions. Building on our previous work of a topologically defined skyrmion number,1 here we demonstrate the conservation of the skyrmion number of hedgehog skyrmions and bimerons under propagation. We furthermore generate tunable multi-skyrmions from superpositions of oppositely polarised Gaussian and split-vortex beams of different waists, and find that the skyrmion number is conserved as a function of waist scaling. For both cases, the topological definition of the skyrmion number forms an intuitive geometric approach to understanding the underlying topology and to identifying the individual skyrmion structures.

Recently investigated free-space optical skyrmion beams have an exciting array of application areas, in particular for material science. Current generation methods typically rely on expensive spatial light modulators and bulky apparatus. We demonstrate a laser source for optical skyrmion beams at red (640nm) and orange (607nm) wavelengths using a praseodymium:YLF gain medium. The interferometric output coupler gave a high-quality first order vortex Laguerre-Gaussian output, which was combined with the fundamental Gaussian output and converted into polarisation skyrmions. Bloch-, N´eel-, and anti-skyrmions were generated, which were propagation stable and had measure skyrmion numbers close to 1. This low-cost and compact source should be useful to diversify optical skyrmion research and could be easily adapted to other laser gain media and wavelengths.

Here, we introduce a framework leveraging a free-space optical system based on the 4f configuration, inspired by the SWIFFT algorithms, designed to significantly enhance the processing of encrypted data using analog optical AI accelerators. This innovative approach aims to outperform traditional electronic machine learning accelerators by offering superior processing speeds and heightened data security. The adoption of the 4f-based optical setup is pivotal, harnessing the natural Fourier transform capabilities of light to efficiently implement complex mathematical operations inherent in hashing and compression algorithms. This alignment with the Fourier transform properties optimizes the system’s computational throughput and energy efficiency, far surpassing conventional electronic processing methods. Furthermore, the utilization of analog optical AI accelerators within this 4f configuration underscores a groundbreaking advancement in processing encrypted data securely and swiftly. The 4f system facilitates parallel processing and high-speed data transmission, characteristics that are instrumental in reducing latency and enhancing the security measures of data processing.

Here, we present a free-space optical communication system, adept at managing alignment deviations and the challenges posed by the atmospheric turbulence in the transmission of spatially structured laser beams, particularly those carrying orbital angular momentum (OAM). The core of our system is tilizing a hybrid convolutional neural network (HCNN). This network is uniquely characterized by the first layer designed as a Fourier optics convolutional layer, implemented optically through a 4f system. This system is dynamically controlled by high-resolution, kilohertz-fast reprogrammable digital micromirror device (DMD). The primary innovation is employing this optical-filtering-based CNN for the training and recognition of multiplexed OAM beams with their unique intensity patterns. The experiments were conducted under conditions simulating atmospheric turbulence based on modified von Kármán model. The system demonstrated promising accuracy, achieving 78.25% under weak turbulence condition and 68.43% in scenarios of strong turbulence.

We demonstrate the use of 3D direct laser writing method to fabricate large-scale 3D metasurfaces with unleashed height degree of freedom. We showcased multiple 3D laser-nanoprinted metasurfaces for a range of photonic applications, including ultrahigh-bandwidth holography, metafibre-enabled optical trapping, highly sensitive molecular sensing, achromatic fibre-optic focusing and imaging, and structured light generation on metafibres. The optical performance of our demonstrated 3D laser-nanoprinted metasurfaces surpass existing 2D metasurfaces fabricated from planar lithography. This metasurface fabrication platform allows superior integration with other photonic elements, such as optical fibres, holding great potential for advanced classical and quantum light manipulation.

Spherulites are crystals with cylindrical crystalline structures and thus exhibit anisotropic optical properties with cylindrical symmetry. Using spherulites, we obtain cylindrical vector optical vortex beams generation and modulations through the spin/orbit conversion. This strategy provides promising opportunities for the spherulite applications in structured light fields.

In this paper, we introduce a simplified technique for the generation of vector beams employing polarization holograms recorded on azo-functionalized copolymer film. The method involves recording two holograms sequentially on the same area of the sample using an interferometer setup. After recording, simply illuminating the hologram with a Gaussian beam from a laser produces a vector beam. By rotating the polarization state of the reading beam, different vector beams on the higher-order Poincare sphere (HOPS) can be generated. This technique is simple, compact, and scalable and holds promising potential in optical information processing applications.

The growing interest in layered transition metal dichalcogenide (TMD) materials stems from their potential applications in valleytronics devices and the ability to control valley polarization. Monolayer molybdenum disulfide (MoS₂), with its optical bandgap of 1.8eV and modulatable valley degree of freedom through circularly polarized light or strain engineering, exhibits distinct characteristics. In this study, we investigate the interaction between structured light possessing orbital angular momentum (OAM) and layered MoS₂. The interaction between optical orbital angular momentum (OAM) and materials has led to the discovery of novel and intriguing physical phenomena, with significant advancements in recent years. In this study, we investigated the resonant Raman spectroscopy of monolayer molybdenum disulfide (MoS₂) under the illumination of light with different orbital angular momentum. Excitation lasers with wavelengths of 633 nm (1.96 eV) and 532 nm (2.33 eV) were utilized, and a spatial light modulator (SLM) was employed to generate light with optical OAM, which was then used to illuminate the monolayer MoS₂ and observe the resulting Raman spectra. The experimental results revealed that, under resonant excitation, an increase in orbital angular momentum caused a blue-shift in the peak positions of the Raman spectra. This finding indicates a strong coupling between excitons and phonons in the material, where the transfer of orbital angular momentum to the layered material results in compressive strain, altering the characteristic Raman peak positions. The insights gained from this study have the potential to enhance the manipulation of spin properties in TMD materials, opening up new possibilities for spin-based optoelectronics.

In this paper we expand and generalise the theoretical work underlying the results presented by F. Castellucci et al. in the paper at Ref. 1, offering an exploration into different regimes of vector light and light matter interaction as well as the inner atomic processes, such as the populations of newly derived partially dressed states which highlight the connection between polarisation and magnetic coupling, and the orbitals they correspond to. This deeper knowledge will not only increase our understanding of how light-atom interaction is impacted by the presence of magnetic fields, and is a step in improving this new method of magnetometry.

We present a series of four experiments unveiling intriguing characteristics of structured beams when interacting with individual, well-localized atoms. The initial investigation explores the placement of a single atom within the dark center of a vortex/doughnut beam, revealing unexpected excitations. Furthermore, the study demonstrates the transfer of the beam’s chirality to the internal and external motion of the atom, as evidenced by alterations in allowed atomic transitions. The research showcases the ability of both intrinsic (polarization) and extrinsic (orbital/structural) angular momentum of the beam to influence the atom, resulting in the transfer of two units of angular momentum. Notably, structured beams induce motion transversal to their propagation direction. The paper concludes with a position-resolved measurement of the azimuthal Doppler shift of a structured beam, uncovering its characteristic divergence at the center and its scale-invariant nature. These findings offer valuable insights into the understanding of structured beam-atom interactions, potentially constituting the first indirect observation of the elusive super-kicks predicted by Barnett and Berry in 2013.

The measurement of the spin angular momentum of circularly polarized light by Beth [Phys. Rev. 50, 115 (1936)] can be explained by using a microscopic torque density. However, the experiment does not resolve the space- and time-dependent evolution of the spin density of light and the wave plate and the covariant form of the microscopic torque density. Here we focus on the covariant description of the helicity, spin, and torque densities of light in materials using the chiral-stress-energy-momentum tensor. We also perform simulations of Gaussian light pulses in quarter-wave-plate geometries made of birefringent and dielectric materials.

A novel approach to creating long-range Structured Laser Beams (SLB) using optical aberrations is described. By combining optical elements that produce significant spherical and defocus aberrations, it is possible to generate an interference field with both transverse and longitudinal local polarization. This creates an SLB that can propagate as a wave to infinity with an invariant transverse profile, different from Bessel Beams (BB). The size and divergence of the central part of the SLB can be much smaller than those observed in Gaussian beams. Experimental confirmation showed a divergence of 0.01 mrad for the central part of the SLB, from a diameter of less than 10 μm. This method makes it possible to form a hollow beam, where non-perpendicular electric and magnetic fields exist in the central part of the beam. An overview of the properties of these SLBs is presented.

This work presents polarization effects caused by the diffraction by patterned polarizing elements, patterned polarizers or patterned retarders. The Fourier transform and Jones matrix formalism is applied to analyze the diffraction pattern. The approach will be applied to analyze simple diffractive elements and vectorial vortex diffraction gratings, as well as for polarizing Fourier transform systems. Theoretical and computational analysis is completed with experimental results using patterned polarizers and spatial light modulators.

The complexity of multiple vortex fields requires an adequate mathematical foundation. We present a modal theory based on Fourier mathematics using cylindrical coordinates. The analysis is analogous to well-known 2D Fourier optics formalism using Cartesian coordinates. The theory is comprehensive in the sense that it cannot only be used to describe and analyze arbitrary vortex fields, but it may also be used for their synthesis. Here, after discussing the basic formalism, we consider various examples of vortex fields, as well as special topics such as the algorithmic design of vortex fields by using computer-generated diffractive optics, self-imaging, and nano-vortices.