Metamaterials, which are composed of metallic and dielectric subwavelength structures arranged in periodic array, are artifi cial materials with the permittivity or permeability less than that of vacuum or with negative values unattainable in nature. [1][2][3] Due to their unique electromagnetic properties, metamaterials have been widely used in many applications, such as sensors, superlenses, miniature antennas, and invisible cloaks. [4][5][6][7] Recently, metamaterial-based perfect absorbers have been attracted considerable attentions and various types of terahertz metamaterial absorbers have been reported. For example, Landy et al. presented a polarization-insensitive metamaterial absorber composed of metallic split ring resonators and cutting wires with singe-band absorption. [ 8 ] X.-J. He et al. proposed a dual-band metamaterial absorber made of two stacked metallic cross resonators and a lower metallic ground plane, separated by an isolation material spacer. [ 9 ] Cheng-Wen Cheng presented wide-angle polarization independent infrared dual band absorbers based on metallic multisized disk arrays. [ 10 ] Yanxia Cui proposed a sawtooth anisotropic metamaterial slab absorber for Transverse Magnetic (TM) polarized light with absorptivity higher than 95% covering a waveband ranging from 3 to 5.5 μ m. [ 11 ] However, current metamaterial absorbers suffer from many disadvantages such as narrow operating waveband, sensitivity to the polarization state of the incident light, narrow accepted angles and a fi xed azimuthal angle, which greatly limit their potential applications to spectroscopic detection and phase imaging. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Hence, a light absorbing device that is broadband, wide-angle and insensitive to the incident light polarization state is urgently needed for its applications in areas mentioned above. In this letter, we propose a two-dimensional (2D) pyramidal shape metamaterial-based absorber. In comparison with previous designs, this pyramid metamaterial absorber has a very high absorptivity performance that is polarization-insensitive, wide-angle and omni-directional at full infrared waveband.The proposed two-dimensional pyramid absorber is composed of alternating metallic and dielectric thin fi lms as shown in the insets of Figure 1 a. The metal thin fi lm is made of gold with thickness t m = 10 nm; dielectric thin fi lm is made of germanium with thickness t d = 190 nm. The total number of metal/dielectric pairs ( N) is 15. These multiple thin fi lm layers are carved into a pyramid structure for each unite cell. The periods of the unit cell in both x and y directions are 1600 nm. A gold fi lm with a thickness ( t = 100 nm) is added under the pyramid metamaterial absorber to block any incident light transmission. The optimized pyramid absorber structure was obtained through fi nite-difference time-domain (FDTD) simulations (Lumerical Inc.). [ 24 ] The material properties of gold and germanium were chosen from the software database-Gold Palik and Ger...

Surface plasmon polaritons (SPPs) has attracted great attention in the last decade and recently it has been successfully applied to nanolithography due to its ability of beyond diffraction limit. This article reviews the recent development in plasmonic nanolithography, which is considered as one of the most remarkable technology for next-generation nanolithography. Nanolithography experiments were highlighted on the basis of SPPs effect. Three types of plasmonic nanolithography methods: contact nanolithography, planar lens imaging nanolithography, and direct writing nanolithography were reviewed in detail, and their advantages and shortages are analyzed and compared, respectively. Finally, the development trend of plasmonic nanolithography is suggested.

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In this study, sea surface air temperature over the Pacific is constructed as a network, and the influences of sea surface temperature anomaly in the tropical central eastern Pacific (El Niño/La Niña) are regarded as a kind of natural attack on the network. The results show that El Niño/La Niña leads an abrupt percolation phase transition on the climate networks from stable to unstable or metastable phase state, corresponding to the fact that the climate condition changes from normal to abnormal significantly during El Niño/La Niña. By simulating three different forms of attacks on an idealized network, including Most connected Attack (MA), Localized Attack (LA) and Random Attack (RA), we found that both MA and LA lead to stepwise phase transitions, while RA leads to a second-order phase transition. It is found that most attacks due to El Niño/La Niña are close to the combination of MA and LA, and a percolation critical threshold Pc can be estimated to determine whether the percolation phase transition happens. Therefore, the findings in this study may renew our understandings of the influence of El Niño/La Niña on climate, and further help us in better predicting the subsequent events triggered by El Niño/La Niña.

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The Talbot effect of an Ag nanolens with five periodic concentric rings that are illuminated by the radially polarized light was numerically studied by means of rigorous finite-difference and time-domain (FDTD) algorithm. It was found that the Talbot effect occurs only when the incident wavelength is at the scale of less than half of period of the grating structures of the nanolenses. Specifically, in this work, the nanolenses with a 500 nm period grating structures has five focal points due to Talbot effect for the incident wavelength of λ = 248 nm. The diameter of the first focal spot after the exit plane in free space is 100 nm. In contrast, we analyzed the corresponding focal points on the basis of Talbot self-imaging by scalar diffraction theory. It was found that the scalar Talbot effect cannot interpret the Talbot effect phenomenon for the metallic nanolenses. It may attribute to the paraxial approximation applied in the Talbot effect theory in far-field region. However, the approximation does not hold in our nanolenses structures during the light propagation. In addition, the Talbot effect appears at the short-wavelength regime only, especially in the ultraviolet wavelength region.

In this work, we studied the air-sea interaction over the tropical central eastern Pacific from a new perspective, climate network. The surface air temperatures over the tropical Pacific were constructed as a network, and the nodes within this network were linked if they have a similar temporal varying pattern. Using three different reanalysis datasets, we verified the percolation phase transition. That is, when the influences of El Niño/La Niña are strong enough to isolate more than 48% of the nodes, the network may abruptly be divided into many small pieces, indicating a change of the network state. This phenomenon was reproduced successfully by a coupled general circulation model, Flexible Global Ocean-Atmosphere-Land System Model Spectral Version 2, but another model, Flexible Global Ocean-Atmosphere-Land System Model Grid-point Version 2, failed. As both models have the same oceanic component, but are with different atmospheric components, the improperly used atmospheric component should be responsible for the missing of the percolation phase transition. Considering that this new phenomenon is only recently noticed, current state-of-the-art models may ignore this process and induce unrealistic simulations. Accordingly, percolation phase transition is proposed as a new test bed, which deserves more attention in the future.

Biomimetic compound eyes with a high numerical aperture on a curved surface were successfully fabricated by intelligent integration of traditional top-down and bottom-up micro- and nanofabrication methods together. In addition, the new hybrid micro- and nanofabrication method allows us to fabricate the antireflective nanostructures on each ommatidium to increase its vision sensitivity by improving the light transmission. The fabricated compound eye was optically characterized and was shown to have a numerical aperture of 0.77 for each ommatidium. Furthermore, it is shown that the transmission of the compound eye can be improved by 2.3% for the wavelength of 632.8 nm and a clearer image can be formed by the fabricated compound eye with antireflective nanostructures compared with that without antireflective nanostructures. In addition, the developed hybrid manufacturing method can be adapted to the fabrication of other complex micro- and nanodevices for photonics or other research areas.