Volume 13, Issue 9

Raman scattering can provide information on molecular fingerprints, which have been widely applied in various fields of material science and nanobiotechnology. Notably, low interference with water molecules in obtaining the Raman spectra between 500 and 2000 cm −1 made it a powerful spectroscopic tool in biology, such as imaging and signaling for a living cell. To be a robust tool for cell biology, the performance of obtaining molecular-specific information with high sensitivity, high resolution in real time, and without inducing cell damage is strongly required. The conventional fluorescence-based method has been suffered from the rapid photobleaching of organic fluorophores and the lack of molecular information. In contrast, Raman scattering is a promising spectroscopic tool to acquire cellular information, and the extremely low signal intensity of Raman scattering could be amplified by incorporating the plasmonic nanomaterials. Along with the fundamental research focus on surface-enhanced Raman scattering (SERS), the practical approaches of SERS for cellular imaging as a new tool for drug screening and monitoring cellular signals have been extensively explored based on new optical setups and new designing strategies for the nanostructures. Diverse nanostructure and surface chemistry for targeting or sensing have been played pivotal roles in acquiring cellular information and high resolution cell imaging. In this regard, this review focused on the recent advances of SERS-based technologies for a live cell imaging investigated such as potential drug screening, signaling for chemicals or biomolecules in cell, in situ sensing, and high spatiotemporal resolution.

The utilization of single molecule electronic devices represents a significant avenue toward advancing next-generation circuits. Recent investigations have notably augmented our understanding of the optoelectronic characteristics exhibited by diverse single molecule materials. This comprehensive review underscores the latest progressions in probing photo-induced electron transport behaviors within molecular junctions. Encompassing both single molecule and self-assembled monolayer configurations, this review primarily concentrates on unraveling the fundamental mechanisms and guiding principles underlying photo-switchable devices within single molecule junctions. Furthermore, it presents an outlook on the obstacles faced and future prospects within this dynamically evolving domain.

The significance of bound states in the continuum (BICs) lies in their potential for theoretically infinite quality factors. However, their actual quality factors are limited by imperfections in fabrication, which lead to coupling with the radiation continuum. In this study, we present a novel approach to address this issue by introducing a merging BIC regime based on a Lieb lattice. By utilizing this approach, we effectively suppress the out-of-plane scattering loss, thereby enhancing the robustness of the structure against fabrication artifacts. Notably, unlike previous merging systems, our design does not rely on the up-down symmetry of metasurfaces. This characteristic grants more flexibility in applications that involve substrates and superstrates with different optical properties, such as microfluidic devices. Furthermore, we incorporate a lateral band gap mirror into the design to encapsulate the BIC structure. This mirror serves to suppress the in-plane radiation resulting from finite-size effects, leading to a remarkable ten-fold improvement in the quality factor. Consequently, our merged BIC metasurface, enclosed by the Lieb lattice photonic crystal mirror, achieves an exceptionally high-quality factor of 10 5 while maintaining a small footprint of 26.6 × 26.6 μm. Our findings establish an appealing platform that capitalizes on the topological nature of BICs within compact structures. This platform holds great promise for various applications, including optical trapping, optofluidics, and high-sensitivity biodetection, opening up new possibilities in these fields.

Photonic reservoir computing (RC) is a simple and efficient neuromorphic computing framework for human cortical circuits, which is featured with fast training speed and low training cost. Photonic time delay RC, as a simple hardware implementation method of RC, has attracted widespread attention. In this paper, we present and experimentally demonstrate a time delay RC system based on a Fabry Perot (FP) laser for multiple tasks processing. Here, the various tasks are attempted to perform in parallel in the multiple longitudinal modes of the FP laser. It is found that the time delay RC system based on the FP laser can successfully handle different tasks across multiple longitudinal modes simultaneously. The experimental results demonstrate the potential of the time delay RC system based on the FP laser to achieve multiple tasks processing, providing various possibilities for improving the information processing ability of neural morphology RC systems, and promoting the development of RC systems.

Hyperbolic phonon polaritons (HPhPs), hybrids of light and lattice vibrations in polar dielectric crystals, empower nanophotonic applications by enabling the confinement and manipulation of light at the nanoscale. Molybdenum trioxide (α-MoO 3 ) is a naturally hyperbolic material, meaning that its dielectric function deterministically controls the directional propagation of in-plane HPhPs within its reststrahlen bands. Strategies such as substrate engineering, nano- and hetero-structuring, and isotopic enrichment are being developed to alter the intrinsic dielectric functions of natural hyperbolic materials and to control the confinement and propagation of HPhPs. Since isotopic disorder can limit phonon-based processes such as HPhPs, here we synthesize isotopically enriched 92 MoO 3 ( 92 Mo: 99.93 %) and 100 MoO 3 ( 100 Mo: 99.01 %) crystals to tune the properties and dispersion of HPhPs with respect to natural α-MoO 3 , which is composed of seven stable Mo isotopes. Real-space, near-field maps measured with the photothermal induced resonance (PTIR) technique enable comparisons of in-plane HPhPs in α-MoO 3 and isotopically enriched analogs within a reststrahlen band (≈820 cm −1 to ≈972 cm −1 ). Results show that isotopic enrichment (e.g., 92 MoO 3 and 100 MoO 3 ) alters the dielectric function, shifting the HPhP dispersion (HPhP angular wavenumber × thickness vs. IR frequency) by ≈−7 % and ≈+9 %, respectively, and changes the HPhP group velocities by ≈±12 %, while the lifetimes (≈3 ps) in 92 MoO 3 were found to be slightly improved (≈20 %). The latter improvement is attributed to a decrease in isotopic disorder. Altogether, isotopic enrichment was found to offer fine control over the properties that determine the anisotropic in-plane propagation of HPhPs in α-MoO 3 , which is essential to its implementation in nanophotonic applications.

Quantum path interferences occur whenever multiple equivalent and coherent transitions result in a common final state. Such interferences strongly modify the probability of a particle to be found in that final state, a key concept of quantum coherent control. When multiple nonlinear and energy-degenerate transitions occur in a system, the multitude of possible quantum path interferences is hard to disentangle experimentally. Here, we analyze quantum path interferences during the nonlinear emission of electrons from hybrid plasmonic and photonic fields using time-resolved photoemission electron microscopy. We experimentally distinguish quantum path interferences by exploiting the momentum difference between photons and plasmons and through balancing the relative contributions of their respective fields. Our work provides a fundamental understanding of the nonlinear photon–plasmon–electron interaction. Distinguishing emission processes in momentum space, as introduced here, could allow nano-optical quantum-correlations to be studied without destroying the quantum path interferences.

We experimentally demonstrate the tuning of accidental bound states in the continuum (A-BICs) in silicon nanodisk arrays. The A-BIC emerges of the destructive interference of multipoles, which are the dominating out-of-plane electric dipole and in-plane magnetic dipole, and weak electric quadrupole and magnetic quadrupole. We further show that the spectral and angular position of the A-BIC can be conveniently tuned by varying the nanodisk size or the lattice period. Remarkably, the angular position can be tuned even to 0°, suggesting an interesting transition of the A-BIC from an off-Γ-BIC to an at-Γ-BIC. Our work provides a new strategy for light trapping with high quality factors, and the obtained tunable A-BICs can find potential applications in low-threshold lasing, enhanced nonlinear optics, and optical sensing.

Amorphous aerogels with the microscopic nanoscale three-dimensional meshes provide superb platforms for investigating unique physicochemical properties. In order to enhance the physical, thermal and mechanical performances, one efficient and common approach is integrating diverse functional materials. Herein, we report a simple strategy to fabricate the amorphous silicon doped Y 2 O 3 aerogels with the post-gelation method under the N 2 /EtOH supercritical atmosphere. The impact of Si concentration on the nonlinear optical properties is investigated for the first time. The maximum modulation depth is 1.65 % with a saturation intensity of 0.78 MW cm −2 with the 1-ps laser excitation at 1590 nm. Finally, we incorporated the silicon-doped Y 2 O 3 aerogel based saturable absorber (SA) into an erbium-doped fiber laser (EDFL) and achieved various mode-locking operations at different wavelengths in the super C band, in terms of the conventional soliton, harmonic soliton molecules pulses, and dual-wavelength soliton mode-locking. Overall, this work confirms that amorphous silicon-doped Y 2 O 3 aerogels are good nonlinear optical materials and pave a way for the ultrafast photonic and nonlinear optical applications with amorphous materials in near future.

Past work has considered the analytic properties of the reflection coefficient for a metal-backed slab. The primary result established a fundamental relationship for the minimal layer thickness to bandwidth ratio achievable for an absorber. There has yet to be establishment of a similar relationship for non-metal-backed layers, and here we present the universal result based on the Kramers–Kronig relations. Our theory is validated with transfer matrix calculations of homogeneous materials, and full-wave numerical simulations of electromagnetic metamaterials. Our results place more general fundamental limits on absorbers and thus will be important for both fundamental and applied studies.

The generation of vector beams using metasurfaces is crucial for the manipulation of light fields and has significant application potential, ranging from classical physics to quantum science. This paper introduces a novel dielectric metasurface composed of quarter-wave plate (QWP) meta-atoms, known as a QWP metasurface, designed to generate focused vector beams (VBs) of Bell-like states under right circularly polarized illumination. The propagation phase imparted on both the co- and cross-polarized components of the output field constructs hyperbolic and helical phase profiles with topological charge l p , whereas the Pancharatnam–Berry (PB) phase acts only on the cross-polarized component to construct another helical phase profile with topological charge l g . Thus, the co- and cross-polarized components form two orthogonal vector vortex (VV) modes with topological charges l p and l p + l g , respectively. When the parameter conditions are satisfied by matching the incident polarization chirality σ and topological charges l p and l g , the focused VBs of Bell-like states are generated by simultaneously manipulating the two VV modes, in contrast to existing QWP metasurfaces. The polarization states of the generated VBs are manipulated using the initial orientation angle θ 0 of the meta-atom. Overall, this research provides an innovative strategy for metasurface design, enhancing the functionality of metasurface devices for a broader range of application scenarios.

Manipulating the thermal emission in the infrared (IR) range significantly impacts both fundamental scientific research and various technological applications, including IR thermal camouflage, information encryption, and radiative cooling. While prior research has put forth numerous materials and structures for these objectives, the significant challenge lies in attaining spatially resolved and dynamically multilevel control over their thermal emissions. In this study, a one-step ultrafast laser writing technique is experimentally demonstrated to achieve position-selective control over thermal emission based on the phase-change material Ge 2 Sb 2 Te 5 (GST). Ultrafast laser writing technique enables direct fabrication and manipulation of laser-induced crystalline micro/nano-structures on GST films. Thermal emission can be precisely controlled by adjusting the pulse energy of the ultrafast laser, achieving a high thermal emissivity modulation precision of 0.0014. By controlling thermal emission, the ultrafast laser writing technique enables multilevel patterned processing. This provides a promising approach for multilevel IR thermal camouflage, which is demonstrated with emissivity-modulated GST emitters. Remarkably, ultrafast laser-induced crystalline micro/nano-structures display geometric grating features, resulting in a diffraction-based structural color effect. This study demonstrates the effective use of laser-printed patterns for storing information in both visible and infrared spectrum.

The manipulation of vector optical fields in three-dimensional (3D) space plays a vital role in both fundamental research and practical implementations of polarization optics. However, existing studies mostly focus on 3D vector optical fields with limited modes. Here, an approach of spin-decoupled spatial partitioning is proposed to generate complex 3D vector optical fields with a customizable number of modes on demand. The crosstalk among different modes is effectively suppressed by the decoupling capability of asymmetric photonic spin–orbit interactions (PSOIs) and the design of region displacement for opposite spin states. As a proof-of-concept demonstration, a metasurface is designed to generate longitudinally varying high-order cylindrical vector fields, ranging from the 2nd to the 10th order in even sequences along the propagation direction. The experimental results demonstrate the effectiveness and potential of our approach to enabling precise control of 3D vector optical fields with arbitrary mode combinations. This work holds promising applications in biophotonics, quantum optics, and communications.

Recently, multifunctional metasurface has showcased its powerful functionality to integrate nanoprinting and holography, and display ultracompact meta-images in near- and far-field simultaneously. Herein, we propose a tri-channel metasurface which can further extend the meta-imaging ranges, with three independent images located at the interface, Fresnel and Fourier domains, respectively. Specifically, a structural-color nanoprinting image is decoded right at the interface of the metasurface, enabled by varying the dimensions of nanostructures; a Fresnel holographic image and another Fourier holographic image are present at the Fresnel and Fourier (far-field) domains, respectively, enabled by geometric phase. The spectral and phase manipulation capabilities of nanostructures have been maximized, and the spatial multiplexing capabilities for diffraction in metasurfaces have also been fully exploited. By leveraging the design freedom enabled through the tuning of the geometric size and orientation of nanostructures, as well as optimizing the diffraction spatial light wave transformation, the encoding of multiple images on the single-celled metasurface is achieved. More interestingly, due to the spatial separation of images across different channels, crosstalk is virtually eliminated, effectively enhancing imaging quality. The proposed metasurface offers several advantages, including a compact design, easiness of fabrication, minimal crosstalk, and high storage density. Consequently, it holds promising applications in image display, data storage, information encryption, anti-counterfeiting, and various other fields.