Black or reflective particles can be trapped in the dark central minimum of a doughnut laser beam produced using a high efficiency computer generated hologram. Such beams carry angular momentum due to the helical wave-front structure associated with the central phase singularity even when linearly polarized. Trapped absorptive particles spin due to absorption of this angular momentum transferred from the singularity beam. The direction of spin can be reversed by changing the sign of the singularity.

Structured light refers to the generation and application of custom light fields. As the tools and technology to create and detect structured light have evolved, steadily the applications have begun to emerge. This roadmap touches on the key fields within structured light from the perspective of experts in those areas, providing insight into the current state and the challenges their respective fields face. Collectively the roadmap outlines the venerable nature of structured light research and the exciting prospects for the future that are yet to be realized.

Particle rotation resulting from the absorption of light carrying angular momentum has been measured. When absorbing CuO particles (1-5μm) were trapped in a focused ‘‘donut’’ laser beam, they rotated, due to the helical phase structure of the beam. Changing the polarization of the light from plane to circular caused the rotation frequency to increase or decrease, depending on the sense of the polarization with respect to the helicity of the beam. Rotation frequencies were obtained by Fourier analysis of amplitude fluctuations in the backscattered light from the particles. © 1996 The American Physical Society.

Almost $100\text{years}$ ago, two different expressions were proposed for the energy-momentum tensor of an electromagnetic wave in a dielectric. Minkowski’s tensor predicted an increase in the linear momentum of the wave on entering a dielectric medium, whereas Abraham’s tensor predicted its decrease. Theoretical arguments were advanced in favor of both sides, and experiments proved incapable of distinguishing between the two. Yet more forms were proposed, each with their advocates who considered the form that they were proposing to be the one true tensor. This paper reviews the debate and its eventual conclusion: that no electromagnetic wave energy-momentum tensor is complete on its own. When the appropriate accompanying energy-momentum tensor for the material medium is also considered, experimental predictions of all various proposed tensors will always be the same, and the preferred form is therefore effectively a matter of personal choice.

We describe a toolbox, implemented in Matlab, for the computational modelling of optical tweezers. The toolbox is designed for the calculation of optical forces and torques, and can be used for both spherical and nonspherical particles, in both Gaussian and other beams. The toolbox might also be useful for light scattering using either Lorenz{Mie theory or the T-matrix method. Computational modelling provides an important bridge between theory and experiment|apart from the simplest cases, computational methods must be used to obtain quantitative results from theory for comparison with experimental results. This is very much the case for optical trapping, where the size range of typical particles trapped and manipulated in optical tweezers occupies the gap between the geometric optics and Rayleigh scattering regimes, necessitating the application of electromagnetic theory. Although, in principle, the simplest cases|the trapping and manipulation of homogeneous and isotropic microspheres|has an analytical solution| generalised Lorenz{Mie theory|signican t computational eort is still required to obtain quantitative results. Unfortunately, the mathematical complexity of Lorenz{ Mie theory presents a signican t barrier to entry for the novice, and is likely to be a major contributor to the lagging of rigorous computational modelling of optical tweezers compared to experiment. If we further consider the calculation of optical forces and torques on non- spherical particles|for example, if we wish to consider optical torques on and rotational alignment of non-spherical microparticles, the mathematical dicult y is considerably greater. Interestingly, one of the most ecien t methods for calculating optical forces