Switchable hybrid-order optical vortex lattice.

Optical vortex (OV) modulation is a powerful technique for enhancing the intrinsic degrees-of-freedom in structured light applications. Particularly, the lattices involving multiple OVs have garnered significant academic interest owing to their wide applicability in optical tweezers and condensed matter physics. However, all OVs in a lattice possess the same order, which cannot be modulated individually, limiting its versatile application. Herein, we propose, to our knowledge, a novel concept, called the hot-swap method, to design a switchable hybrid-order OV lattice, in which each OV is easily replaced by arbitrary orders. We experimentally generated the switchable hybrid-order OV lattice and studied its characteristics, including interferograms, retrieved phase, energy flow, and orbital angular momentum. Furthermore, the significant advantages of the switchable hybrid-order OV lattice are demonstrated through the independent manipulation of multiple yeast cells. This study provides a novel scheme for accurate control and modulation of OV lattices, which greatly facilitates the diverse applications of optical manipulation and particle trapping and control.

Generation of arbitrarily structured optical vortex arrays based on the epicycle model.

Optical vortex arrays (OVAs) are complex light fields with versatile structures that have been widely studied in large-capacity optical communications, optical tweezers, and optical measurements. However, generating OVAs with arbitrary structures without explicit analytical expressions remains a challenge. To address this issue, we propose an alternative scheme for customizing OVAs with arbitrary structures using an epicycle model and vortex localization techniques. This method can accurately generate an OVA with an arbitrary structure by pre-designing the positions of each vortex. The influence of the number and coordinates of the locating points on customized OVAs is discussed. Finally, the structures of the OVA and each vortex are individually shaped into specifically formed fractal shapes by combining cross-phase techniques. This unique OVA will open up novel potential applications, such as the complex manipulation of multiparticle systems and optical communication based on optical angular momentum.

Generation of discrete higher-order optical vortex lattice at focus.

Higher-order vortices (HOVs) extend the dimensions of optical vortex regulation, which is of great significance in optical communication and optical tweezers. Herein, we demonstrate an alternative scheme to produce a HOV in the focus plane using multiple Laguerre-Gaussian (LG) beam interference, termed a discrete higher-order optical vortex lattice (DHOVL). The modulation depth of the DHOVL exceeds 2π. In this case, the topological charge (TC) of the DHOVL is determined by the difference of the phase period between the innermost and the outermost interference beams. Compared with a conventional HOV (CHOV), the vortex exists in a form of multiple unit singularities sharing a dark core. In addition, the average orbital angular momentum per photon of the DHOVL increases with increasing TC, surpassing that of the CHOV. This work provides a novel, to the best of our knowledge, scheme to produce a HOV, which will facilitate several advanced applications, including optical micromanipulation, optical sensing and imaging, and optical fabrication.

When optical vortex array meets cycloid.

Optical vortex arrays (OVAs) have drawn widespread attention owing to their multiple optical vortices and higher dimensions. However, existing OVAs have not yet been utilized to exploit the synergy effect as an entire system, particularly for manipulating multiple particles. Thus, the functionality of OVA should be explored to respond to application requirements. Hence, this study proposes a functional OVA, called cycloid OVA (COVA), based on a combination of cycloid and phase-shift techniques. By modifying the cycloid equation, multiple structural parameters are designed to modulate the structure of the COVAs. Subsequently, versatile and functional COVAs are experimentally generated and modulated. In particular, COVA executes local dynamic modulation, whereas the entire structure remains unchanged. Further, the optical gears are first designed using two COVAs, which exhibit potential for transferring multiple particles. Essentially, OVA is endowed the characteristics and capacity of the cycloid when they meet. This work provides an alternative scheme to generate OVAs, which will open up advanced applications for the complex manipulation, arrangement and transfer of multiple particles.

Cycloid-structured optical tweezers.

We designed novel cycloid-structured optical tweezers based on a modified cycloid and holographic shaping techniques. The optical tweezers realize all the dynamic characteristics of the trapped particles, including start, stop, and variable-velocity motions along versatile trajectories. The superiority of the tweezers is experimentally verified using polystyrene micro-sphere manipulation. This work provides a novel platform for more complex manipulations of particles.

Crucial roles of graphene oxide in preparing alginate/nanofibrillated cellulose double network composites hydrogels.

In this study, a novel strategy to prepare sodium alginate (SA)/nano fibrillated cellulose (NFC) double network (DN) hydrogel beads with the aid of graphene oxide (GO) was developed. In comparison with the multi-step freezing-thawing method, this study employs a facile one-step freeze drying method with the presence of GO sheets. The crucial roles of GO were highlighted as an efficient nucleating agent of NFC and a reinforcer for the hydrogel. The adsorption property of the DN hydrogel towards crystal violet (CV) was also studied. Results indicated that the introduction of GO could greatly facilitate the formation of double networks. Furthermore, the as-prepared DN hydrogel beads exhibited an efficacious adsorption property towards CV. The maximum adsorption capacity of the hydrogels for CV was observed as 665 mg g-1. Therefore, our approach here represents a facile method for the preparation of crystalline polymer based DN hydrogels to replace the awkward freezing-thawing process, giving inspiration for DN hydrogels design and preparation. Moreover, due to its efficient adsorption capacity, the hydrogels hold great promise for the water pollution control materials.

Close-packed optical vortex lattices with controllable structures.

As a spatial structured light field, the optical vortex (OV) has attracted extensive attention in recent years. In practice, the OV lattice (OVL) is an optimal candidate for applications of orbital angular momentum (OAM)-based optical communications, microparticle manipulation, and micro/nanofabrication. However, traditional methods for producing OVLs meet a significant challenge: the OVL structures cannot be adjusted freely and form a close-packed arrangement, simultaneously. To overcome these difficulties, we propose an alternative scheme to produce close-packed OVLs (CPOVLs) with controllable structures. By borrowing the concept of the close-packed lattice from solid-state physics, CPOVLs with versatile structures are produced by using logical operations of expanding OV primitive cells combined with the technique of phase mask generation. Then, the existence of OAM states in the CPOVLs is verified. Furthermore, the energy flow and OAM distribution of the CPOVLs are visualized and analyzed. From a light field physics viewpoint, this work increases the adjustment dimensions and extends the fundamental understanding of the OVL, which will introduce novel applications.

Controllable mode transformation in perfect optical vortices.

We report a novel method to freely transform the modes of a perfect optical vortex (POV). By adjusting the scaling factor of the Bessel-Gauss beam at the object plane, the POV mode transformation can be easily controlled from circle to ellipse with a high mode purity. Combined with the modulation of the cone angle of an axicon, the ellipse mode can be freely adjusted along the two orthogonal directions. The properties of the "perfect vortex" are experimentally verified. Moreover, fractional elliptic POVs with versatile modes are presented, where the number and position of the gaps are controllable. These findings are significant for applications that require the complex structured optical field of the POV.

Broadband near-infrared quantum cutting by Ce-Yb codoped YAG transparent glass ceramics for silicon solar cells.

Ce3+-Yb3+ co-doped transparent glass ceramics containing YAG nanocrystals were prepared by a conventional melt-quenching method. Broadband near infrared quantum cutting was achieved in the glass ceramics and proved to be a cooperative down-conversion process. Under 460 nm excitation, 2F5/2 to 5d1 electronic transitions occurred in Ce3+ and transferred their energy to two neighboring Yb3+. The dependence of the luminescence spectra and decay curves on Yb3+ concentration was investigated to understand the energy transfer mechanism. The energy transfer efficiency and the down-conversion quantum efficiency were estimated to be as high as 77.8% and 177.8%, respectively. This work will open a new route towards increased efficiency in silicon solar cells.

Broadband ultraviolet to near infrared conversion in Eu2+,Nd3+ co-doped SrAl2O4.

In this study, we investigated the quantum cutting (QC) mechanism in Eu2+-Nd3-co-doped SrAl2O4 microcrystals by fluorescence spectroscopy and decay lifetime analysis. In this material, the near-infrared (NIR) emissions of Nd3+ in the range of 800-1200 nm were enhanced under the excitation of the Eu2+:4f7 → 4f65d1 transition radiation. The lifetime of the 5d1 level of Eu2+ decreased with the increase in the Nd3+ concentration. These results verified the occurrence of cooperative energy transfer (CET) from the Eu2+:5d1 excited state to the Nd3+:4F3/2 level, by which one absorbed ultraviolet-visible photon was converted to two NIR photons with an optimal quantum efficiency (QE) of approximately 177.1%. Therefore, this broadband QC material paves the way for a further increase in the conversion efficiency of c-Si solar cells.

In situ measurement of the topological charge of a perfect vortex using the phase shift method.

We propose a method to determine the topological charge (TC) of a perfect vortex. With the phase shift technique, the perfect vortex and its conjugate beam exactly overlap and interfere. Consequently, the TC of a perfect vortex is determined by counting the number of interference fringes. This proposed method enables in situ determination of the TC of the perfect vortex without the need for additional optical elements, and it is immune to environmental vibration and parasitic interference.