Spin-Orbit Angular-Momentum Transfer from a Nanogap Surface Plasmon to a Trapped Nanodiamond

Nanoscale Helical Optical Force for Determining Crystal Chirality

The deterministic control of material chirality has been a sought-after goal. As light possesses intrinsic chirality, light-matter interactions offer promising avenues for achieving non-contact, enantioselective optical induction, assembly, or sorting of chiral entities. However, experimental validations are confined to the microscale due to the limited strength of asymmetrical interactions within sub-diffraction limit ranges. In this study, a novel approach is presented to facilitate chirality modulation through chiral crystallization using a helical optical force field originating from localized nanogap surface plasmon resonance. The force field emerges near a gold trimer nanogap and is propelled by linear and angular momentum transfer from the incident light to the resonant nanogap plasmon. By employing Gaussian and Laguerre-Gaussian incident laser beams, notable enantioselectivity is achieved through low-power plasmon-induced chiral crystallization of an organic compound-ethylenediamine sulfate. The findings provide new insights into chirality transmission orchestrated by the exchange of linear and angular momentum between light and nanomaterials.

Mie-Resonant Nanophotonic-Enhancement of Asymmetry in Sodium Chlorate Chiral Crystallization

Studies on chiral spectroscopy have recently demonstrated strong enhancement of chiral light-matter interaction in the chiral near-field of Mie resonance in high-refractive-index dielectric nanostructures by studies on chiral spectroscopy. This situation has motivated researchers to demonstrate effective chiral photosynthesis under a chiral near-field beyond circularly polarized light (CPL) as a chiral source. However, the effectivity of the chiral near-field of Mie resonance for chiral photosynthesis has not been clearly demonstrated. One major challenge is the experimental difficulty in evaluating enantiomeric excess of a trace amount of chiral products synthesized in the near-field. Here, by adopting sodium chlorate chiral crystallization as a phenomenon that includes both synthesis and the amplification of chiral products, we show that crystallization on a Mie-resonant silicon metasurface excited by CPL yields a statistically significant large crystal enantiomeric excess of ∼18%, which cannot be achieved merely by CPL. This result provides implications for efficient chiral photosynthesis in a chiral near-field.

Switchable rotation of metal nanostructures in an intensity chirality-invariant focus field

Light-induced rotation is a fundamental motion form that is of great significance for flexible and multifunctional manipulation modes. However, current optical rotation by a single optical field is mostly unidirectional, where switchable rotation manipulation is still challenging. To address this issue, we demonstrate a switchable rotation of non-spherical nanostructures within a single optical focus field. Interestingly, the intensity of the focus field is chiral invariant. The rotation switch is a result of the energy flux reversal in front and behind the focal plane. We quantitatively analyze the optical force exerted on a metal nanorod at different planes, as well as the surrounding energy flux. Our experimental results indicate that the direct switchover of rotational motion is achievable by adjusting the relative position of the nanostructure to the focal plane. This result enriches the basic motion mode of micro-manipulation and is expected to create potential opportunities in many application fields, such as biological cytology and optical micromachining.

Full-space wavefront manipulation enabled by asymmetric photonic spin-orbit interactions

Optical metasurfaces empower complete wavefront manipulation of electromagnetic waves and have been found in extensive applications, whereas most of them work in either transmission or reflection space. Here, we demonstrate that two independent and arbitrary phase profiles in transmission and reflection spaces could be produced by a monolayer all-dielectric metasurface based on the asymmetric photonic spin-orbit interactions, realizing full-space wavefront independent manipulation. Furthermore, the supercell-based non-local approach is employed to suppress crosstalk between adjacent nanopillars in one supercell for broadband and high-efficiency wavefront manipulation in full space. Compared with the conventional unit cell-based local approach, such a method could improve efficiency about 10%. As a proof of concept, two metadevices are designed, in which the maximum diffraction efficiencies are ∼95.53%/∼74.07% within the wavelength range of 1500-1600 nm in reflection/transmission space under circularly polarized light incidence. This configuration may offer an efficient way for 2π-space holographic imaging, augmented reality, virtual reality technologies, three-dimensional imaging, and so forth.

Controllable transportation of microparticles along structured waveguides by the plasmonic spin-hall effect

With the nanoscale integration advantage of near field photonics, controllable manipulation and transportation of micro-objects have possessed plentiful applications in the fields of physics, biology and material sciences. However, multifunctional optical manipulation like controllable transportation and synchronous routing by nano-devices are limited and rarely reported. Here we propose a new type of Y-shaped waveguide optical conveyor belt, which can transport and route particles along the structured waveguide based on the plasmonic spin-hall effect. The routing of micro-particles in different branches is determined by the optical force components difference at the center of the Y junction along the two branches of the waveguide. The influence of light source and structural parameters on the optical forces and transportation capability are numerically studied. The results illustrate that the proposed structured waveguide optical conveyor belt can transport the microparticles controllably in different branches of the waveguide. Due to the selective transportation ability of microparticles by the 2D waveguide, our work shows great application potential in the region of on-chip optical manipulation.

Energy flow inversion in an intensity-invariant focusing field

Dependence of light intensity on energy flow is the most intuitive presentation of an optical field. This dependence, however, also limits the applications to the interaction of the light field with matter. For further insight into this, we demonstrate a novel case of the optical field, named as the counterintuitive chiral intensity field (CCIF), in the highly focusing situation: the energy flow reverses during the propagation but the intensity distribution pattern is kept approximately invariant. Our results show that, in this process, the mode correlation decreases rapidly while the intensity correlation remains invariant in the focus area. Furthermore, this property is still valid even if the pattern helicity and number of spiral arms are changed. This work deepens the understanding of the relationship between energy flow and field intensity, and it will offer diversified operations in many applications, such as optical micromanipulation, optical fabrication, etc.