Semidiscrete optical vortex droplets in quasi-phase-matched photonic crystals

A new scheme for producing semidiscrete self-trapped vortices (\textquotedblleft swirling photon droplets\textquotedblright ) in photonic crystals with competing quadratic ($\chi ^{(2)}$) and self-defocusing cubic ($\chi ^{(3)}$) nonlinearities is proposed. The photonic crystal is designed with a striped structure, in the form of spatially periodic modulation of the $\chi ^{(2)}$ susceptibility, which is imposed by the quasi-phase-matching technique. Unlike previous realizations of semidiscrete optical modes in composite media, built as combinations of continuous and arrayed discrete waveguides, the semidiscrete vortex droplets are produced here in the fully continuous medium. This work reveals that the system supports two types of semidiscrete vortex droplets, \textit{viz}., onsite- and intersite-centered ones, which feature, respectively, odd and even numbers of stripes, $\mathcal{N}$. Stability areas for the states with different values of $\mathcal{N}$ are identified in the system's parameter space. Some stability areas overlap with each others, giving rise to multistability of states with different $\mathcal{N}$. The coexisting states are mutually degenerate, featuring equal values of the Hamiltonian and propagation constant. An experimental scheme to realize the droplets is outlined, suggesting new possibilities for the long-distance transmission of structured light carrying orbital angular momentum in nonlinear media.Comment: 9 pages, 7 figures, and 82 reference

Generation of ultrafast tunable super-oscillation light fields

In this paper, we conceptually propose and numerically demonstrate the generation of ultrafast tunable super-oscillation (SO) light fields by tightly focusing a radially polarized Gaussian femtosecond pulse laser. It is shown that, as the fleeting time goes on within one-half cycle (0 fs 0.61λ/NA, where λ is the wavelength of incident beam and NA is the numerical aperture of objective lens), via a SO spot (<0.36λ/NA), to a super-resolved spot (<0.5λ/NA). We further uncover the rapid evolutions on the full width at half maximum, the normalized central intensity, and the side lobe of focused superoscillatory spots, thus supporting ultrafast adjustable SO light fields. In addition, the effect of primary spherical aberration on the focusing properties of SO spots is examined. The associated mechanism to yield such time-varying SO light fields is elucidated as well. The results presented here expand the flexibility of ultrafast light field manipulation and hold extensive applications in ultrafast and super-resolved imaging, high-density optical data storage, and high-efficiency particle trapping

Recent advances on optical vortex generation

This article reviews recent progress leading to the generation of optical vortex beams. After introducing the basics of optical vortex beams and their promising applications, we summarized different approaches for optical vortex generation by discrete components and laser cavities. We place particular emphasis on the recent development of vortex generation by the planar phase plates, which are able to engineer a spiral phasefront via dynamic or geometric phase in nanoscale, and highlight the independent operation of these two different phases which leads to a multifunctional optical vortex beam generation and independent spin-orbit interaction. We also introduced the recent progress on vortex lasing, including vortex beam generation from the output of bulk lasers by modification of conventional laser cavities with phase elements and from integrated on-chip microlasers. Similar approaches are also applied to generate fractional vortex beams carrying fractional topological charge. The advanced technology and approaches on design and nanofabrications enable multiple vortex beams generation from a single device via multiplexing, multicasting, and vortex array, open up opportunities for applications on data processing, information encoding/decoding, communication and parallel data processing, and micromanipulations

WO₃-LaFeO₃ Nanocomposites for Highly Sensitive Detection of Acetone Vapor at Low Operating Temperatures

The development of a rapid, highly sensitive, and dependable acetone sensor holds significant importance for human health and safety. To enhance the acetone sensing performance of LaFeO3 nanoparticles for practical applications, commercial n-type WO3 nanoparticles were incorporated as additives. They were directly mixed with LaFeO3 nanoparticles produced through a sol-gel method, creating a series of WO3-LFO nanocomposites with varying mass ratios. These nanocomposites were characterized using XRD, SEM, BET, and XPS techniques. Compared to pure LFO nanoparticles, the prepared nanocomposites exhibited larger specific surface areas with enhanced surface reactivity. The introduction of p-n heterojunctions through the mixing process improved the regulation of acetone molecules on internal carrier conduction within nanocomposites. As a result, the nanocomposites demonstrated superior acetone sensing performance in terms of optimal operating temperature, vapor response value, selectivity, and response/recovery speed. Notably, the nanocomposites with a 5wt% addition of WO3 showed the lowest optimal operating temperature (132 °C), the fastest response/recovery speed (28/9 s), and the highest selectivity against ethanol, methanol, and EG. On the other hand, the nanocomposites with a 10wt% addition of WO3 displayed the maximum vapor response value (55.1 to 100 ppm) at an optimal operating temperature of 138 °C, along with relatively good repeatability, stability, and selectivity

All-optical vectorial control of multistate magnetization through anisotropy-mediated spin-orbit coupling

The interplay between light and magnetism is considered as a promising solution to fully steer multidimensional magnetic oscillations/vectors, facilitating the development of all-optical multilevel recording/memory technologies. To date, impressive progress in multistate magnetization instead of a binary level has been witnessed by primarily resorting to double laser beam excitation. Yet, the control mechanisms are limited to specific magnetic medium or intricate optical configuration as well as overlooking the crystallographic architecture of the media and the polarization-phase linkage of the light fields. Here, we theoretically present a novel all-optical strategy for generating arbitrary multistate magnetization through the inverse Faraday effect. This is achieved by strongly focusing a single vortex-phase configured beam with circular polarization onto the anisotropic magnetic medium. By judiciously tuning the topological charge effect, the optical anisotropic effect, and the anisotropic optomagnetic effect, the light-induced magnetic vector can be flexibly redistributed between its transverse and longitudinal components, thus enabling orientation-unlimited multilevel magnetization control. In this optomagnetic process, we also reveal the role of anisotropy-mediated spin-orbit coupling, another physical mechanism that enables the effective translation of the angular momentum of light fields to the magnetic system. Furthermore, the conceptual paradigm of all-optical multistate magnetization is verified. Our findings show great prospect in multidimensional high-density optomagnetic recording and memory devices and also in high-speed information processing science and technology

Anomalous upconversion luminescence of SrMoO₄:Yb³⁺/Er³⁺ nanocrystals by high excited state energy transfer

The SrMoO₄:Yb³⁺/Er³⁺ nanocrystals (NCs) were synthesized by sol-gel method. The upconversion luminescence properties of SrMoO₄:Yb³⁺/Er³⁺ NCs were studied in contrast to the identical dopants in Y₂O₃ NCs under the same experimental conditions. The results demonstrate that the green emission intensity of the former is much stronger than that of the latter, while the red emission intensity is reverse. Interestingly, the green-to-red intensity ratio of SrMoO₄:Yb³⁺/Er³⁺ NCs increases with the increase of Yb³⁺ concentration at fixed Er³⁺ concentration. The anomalous luminescence properties of SrMoO₄:Yb³⁺/Er³⁺ NCs are attributed to the high excited state energy transfer (HESET) from the |²F₇/₂, ³T₂> state of the sensitizer Yb³⁺−MoO₄²⁻ dimer to the ⁴F₇/₂ level of the activator Er³⁺. The HESET process can partly decrease the lattice phonon quenching processes at lower energy levels of Er³⁺ and enhance the green emission dramatically.6 page(s

Three-dimensional supercritical resolved light-induced magnetic holography

In the era of big data, there exists a growing gap between data generated and storage capacity using two-dimensional (2D) magnetic storage technologies (for example, hard disk drives), because they have reached their performance saturation. 3D volumetric all-optical magnetic holography is emerging rapidly as a promising road map to realizing high-density capacity for its fast magnetization control and subwavelength magnetization volume. However, most of the reported light-induced magnetization confronts the problems of impurely longitudinal magnetization, diffraction-limited spot, and uncontrollable magnetization reversal. To overcome these challenges, we propose a novel 3D light-induced magnetic holography based on the conceptual supercritical design with multibeam combination in the 4π microscopic system. We theoretically demonstrate a 3D deep super-resolved Embedded Image purely longitudinal magnetization spot by focusing six coherent circularly polarized beams with two opposing high numerical aperture objectives, which allows 3D magnetic holography with a volumetric storage density of up to 1872 terabit per cubic inches. The number and locations of the super-resolved magnetization spots are controllable, and thus, desired magnetization arrays in 3D volume can be produced with properly designed phase filters. Moreover, flexible magnetization reversals are also demonstrated in multifocal arrays by using different illuminations with opposite light helicity. In addition to data storage, this magnetic holography may find applications in information security, such as identity verification for a credit card with magnetic stripe.NRF (Natl Research Foundation, S’pore)ASTAR (Agency for Sci., Tech. and Research, S’pore)Published versio