A high absorption broadband absorber based on MXene and tungsten nanospheres in visible and near-infrared bands is proposed. The absorber has a maximum absorption of 100% and an average absorption of 95% in the wavelength range of 400–2500 nm. The theoretical mechanism and parameter adjustability of the absorber are analyzed by FDTD solutions. The results show that the structural parameters can effectively adjust the absorption performance. The good absorption performance is due to the action of the local surface plasmon resonance coupling with the gap surface plasmon resonance and Fabry–Perot resonance. The simulation results show that the absorber is insensitive to the polarization and oblique incidence angle of incident light, and that high absorption and broadband can be maintained when the oblique incidence angle is up to 60°.

The multi-channel high-efficiency absorber in the mid-infrared band has broad application prospects. Here, we propose an SiC-photonic crystal (PhC) heterostructure-SiC structure to realize the absorber. The absorption characteristics of the structure are studied theoretically. The results show that the structure can achieve high-efficiency multi-channel absorption in the mid-infrared range. The absorption peaks come from the coupling of the dual Tamm phonon polariton (TPhP) mode formed at the interface between the two SiC layers and the photonic crystal, and the optical Tamm state (OTS) mode formed in the PhC heterostructure. By adjusting the thickness of the air dielectric layer and the period of the PhC in the heterostructure, the mode coupling intensity can be regulated; thereby, the position and intensity of the absorption peak can be adjusted. In addition, the absorption peaks of TE and TM polarized light can be controlled by changing the incident angle. Adjusting the incident angle can also control the excitation and intensity of the epsilon-near-zero (ENZ) phonon polariton mode produced by TM polarized light. This kind of light absorber may have potential applications in sensors, filters, modulators, switches, thermal radiators, and so on.

The nonlinear refraction of silver nanoparticles (AgNPs) in n-hexane was studied by using the closed-aperture Z-scan technique with a 532 nm nanosecond laser. It was found that, the nonlinear refraction of AgNPs shows the coexistence and transformation from self-focusing to self-defocusing. Specifically, self-focusing occurs at low excitation intensity, self-defocusing occurs at high excitation intensity, and coexistence of self-focusing and self-defocusing occurs at relatively moderate excitation intensity. The experimental results were analysed and discussed in terms of third-order and fifth-order nonlinear refractive effect. Specifically, the self-focusing is caused by the positive third-order nonlinear refraction, the self-defocusing is induced by the negative fifth-order nonlinear refraction, and the transformation from the self-focusing to self-defocusing at medium excitation intensity is caused by the competition of third-order and fifth-order nonlinear refraction. Finally, the third-order refractive index and fifth-order refractive index were obtained.

In this work, we propose a novel transformer-based deep learning model for the design of electromagnetically induced transparency (EIT) metasurfaces, which consists of a forward network to predict transmission spectra from structural parameters and an inverse network to retrieve structural parameters from target spectra. To train the model, we generated a dataset of 23,500 samples by automating CST simulations. The well-trained model can predict all seven structural parameters of an EIT metasurface from a given target spectrum within milliseconds, achieving a mean square error (MSE) of 8.49 × 10⁻⁴ at convergence. The mean errors between the predicted data and target parameters remain below 0.25 μm. The relative spectral error (RSE) is employed to evaluate the discrepancy between the spectra from predicted structures and the targets, with a maximum RSE of 0.57%. Benchmarking against two other neural networks confirms the superior predictive capability and accuracy of our model. Furthermore, the method not only streamlines EIT metasurface design but is readily adaptable to diverse metasurface devices across the electromagnetic spectrum, establishing a versatile platform for metasurface inverse design.

We propose an absorber composed of graphene and vanadium dioxide (VO₂). The phase transition of VO₂ enables dynamic switching of the absorption response between a single broadband state and three narrowband states. The results indicate that when VO₂ changes to the metallic state, the absorber exhibits triple narrow band absorption. When VO₂ is in the dielectric phase, the absorber demonstrates single broadband absorption. The absorption can be regulated through the Fermi energy level (E_F) of graphene. Furthermore, the proposed absorber exhibits polarization-independent characteristics and maintains stable absorption performance under wide-angle oblique incidence. The absorber also has high refractive index sensitivity. Impedance matching theory is employed to investigate the physical mechanism governing the absorber. The tuning principle of the device was analyzed and verified successfully by using an equivalent circuit model (ECM).

Nonlinear absorption (NLA) in silver nanoparticles (Ag NPs) is strongly affected by plasmonic field enhancement. However, its wavelength- and energy-dependent evolution on the red side of the surface plasmon resonance (SPR) band remains insufficiently understood. Here, we systematically investigate the NLA properties of Ag NPs using open-aperture (OA) Z-scan measurements combined with femtosecond transient absorption (TA) spectroscopy. The results show that Ag NPs exhibit saturable absorption (SA) under low excitation energies, whereas higher excitation energies induce a mixed SA/reverse saturable absorption (RSA) response. A pronounced wavelength dependence is also observed as the excitation approaches the SPR band, where nonlinear absorption gradually evolves with spectral detuning. TA measurements revealed ultrafast carrier dynamics characterized by a fast electron–phonon relaxation process (~3.3 ps) followed by a slower lattice cooling process (~46 ps). These results demonstrate that the nonlinear response is governed by the interplay between plasmonic resonance and ultrafast carrier relaxation, providing insights for the design of plasmonic nanomaterials for ultrafast nonlinear photonic applications.