The emerging meta-holograms rely on arrays of intractable meta-atoms with various geometries and sizes for customized phase profiles that can precisely modulate the phase of a wavefront at an optimal incident angle for given wavelengths. The stringent and band-limited angle tolerance remains a fundamental obstacle for their practical application, in addition to high fabrication precision demands. Utilizing a different design principle, we determined that facile metagrating holograms based on extraordinary optical diffraction can allow the molding of arbitrary wavefronts with extreme angle tolerances (near-grazing incidence) in the visible–near-infrared regime. By modulating the displacements between uniformly sized meta-atoms rather than the geometrical parameters, the metagratings produce a robust detour phase profile that is irrespective of the wavelength or incident angle. The demonstration of high-fidelity meta-holograms and in-site polarization multiplexing significantly simplifies the metasurface design and lowers the fabrication demand, thereby opening new routes for flat optics with high performances and improved practicality.

We analytically show that an incident light can be almost completely diffracted into the −1^st order in wide-angle and broadband by suitably designed thin metallic nano-gratings with simple rectangular cross sections. Such extraordinary optical diffraction results from the excitation of localized cavity modes and exists even when the grating period is modulated in a broad range. By modulating the period with binary holography techniques, we can shape an incident wave into arbitrary wavefronts with near-unity conversion efficiencies. To show the efficacy of this approach, we demonstrate three reflection-type metasurfaces for achieving near-complete conversions from a Gaussian beam into a focused beam, Bessel beam, and vortex beam, respectively, with the complete suppression of the undesired specular reflection. Our findings provide a facile approach to build arbitrary wavefront-shaping metasurfaces with wide-angle, broadband, and high efficiency performance.

We show that a metasurface composed of a subwavelength metallic slit array embedded in an asymmetric dielectric environment can exhibit either extraordinary optical transmission (EOT) or extraordinary optical diffraction (EOD). The cascaded refractive indices of the dielectrics can leverage multiple decaying passages into variant subsections with different diffraction order combinations according to the diffraction order chart in the k-vector space, providing a flexible mean to tailor resonance decaying pathways of the metallic slit cavity mode by changing the wavevector of the incident light. As a result, either the zeroth transmission or $-1$st reflection efficiencies can be enhanced to near unity by the excitation of the localized slit cavity mode, leading to either EOT or EOD in a single structure, depending on the illumination angle. Based on this appealing feature, a multifunctional metasurface that can switch its functionality between transmission filter, mirror, and off-axis lens is demonstrated. Our findings provide a convenient way to construct multifunctional miniaturized optical components on a single planar device.

We have demonstrated that a typical nanothermometer was incorporated in a bovine serum albumin stabilized gold nanostar-indocyanine green (denoted as GNS-ICG-BSA) nanoprobe to realize surface-enhanced Raman scattering (SERS) imaging-based real-time sensitive monitoring of intracellular temperature in photothermal therapy (PTT), which significantly improved the spatial resolution compared to infrared thermal imaging. Herein, an exogenous thermosensitive molecule, ICG, acting as a tri-functional agent, was selected as the Raman reporter instead of direct cellular biochemical changes. The triggering of the obtained probe was unaffected by the cellular microenvironment, so it can act as a monitor of PTT in various cell types. High-resolution mass spectrometry (HRMS) was used to investigate the thermosensitive mechanism of ICG. The actively targeted GNS-ICG-BSA nanotags were used to induce SERS mapping-guided in vitro PTT of U87 glioma cells. Meanwhile, small temperature variations within a cell during PTT can be precisely monitored through the SERS fingerprint information, with a spatial resolution at the subcellular level and a sensitivity of 0.37 °C. Thus, the integrated GNS-ICG-BSA nanotags can be treated as a theranostic probe, a SERS imaging probe and an intracellular thermometer. Moreover, the good biocompatibility and the low cytotoxicity of GNS-ICG-BSA nanotags, together with their superior photothermal ablation effect on U87 glioma cells have been confirmed. This suggested that the implanted nanothermometry approach would be promising for a better understanding of the biological processes at subcellular level and provide new insights into the fabrication of a multifunctional nanoplatform. Furthermore, this study revealed that the SERS-based monitoring technique can offer great potential for theranostics as an emerging strategy.

We present an approach to build multiwavelength achromatic metasurface that can work in off-axis configuration with an ultra-wide applicable incident angle range for visible light. The metasurface is constructed by combining multiple metallic nano-groove gratings, which support enhanced diffractions for transverse magnetic polarization in an ultrawide incident angle range from 10° to 80° due to the excitations of localized gap plasmon modes at different resonance wavelengths. To achieve the achromatic diffraction, the ratio between the resonance wavelength and the period of each elementary grating is fixed. Incident light at those multiple resonance wavelengths can be efficiently diffracted into the same direction with near-complete suppression of the specular reflection. Based on the similar approach, we also design a wide-angled off-axis achromatic flat lens for focusing light of different wavelengths into the same position. Our findings provide an alternative simple way to design various off-axis achromatic flat optical elements without stringent angle requirement for imaging and display applications.

Negative refraction, an unnatural optical phenomenon in which the incident and the refracted waves reside on the same side of the surface normal, has been demonstrated with the invention of negative index media based on artificially engineered photonic structures called metamaterials. It has received wide attention due to its potential applications in imaging, nonlinear optics, and electromagnetic cloaking. However, it is highly challenging to realize negative refraction operating at all angles and with the perfect transmission. In this work, leveraging the recent development in topological photonics, we propose to realize reflectionless negative refraction for all incident angles with a topological metamaterial. The proposed metamaterial possesses two Weyl points of opposite topological charges. By interfacing the metamaterial with a perfect electric conductor (PEC) or a perfect magnetic conductor (PMC), the Fermi arc connecting the two Weyl points can take the form of a half-circle possessing a positive or a negative refractive index. Importantly, due to the topological protection, there is no reflection at the interface between the PEC and PMC covered areas, leading to the observation of all-angle negative refraction without reflection at the boundary. Our work provides a new platform for manipulating the propagation of surface waves, which may find applications in the construction of integrated photonic devices.