A reactive electron beam evaporation process was used to fabricate 1.064 μm HfO2/SiO2 high reflectors. The deposition process was optimized to reduce the nodular density. Cross-sectioning of nodular defects by a focused ion-beam milling instrument showed that the nodule seeds were the residual particles on the substrate and the particulates from the silica source "splitting." After optimizing the substrate preparation procedure and the evaporation process, a low nodular density of 2.7/mm2 was achieved. The laser damage test revealed that the ejection fluences and damage growth behaviors of nodules created from deep or shallow seeds were totally different. A mechanism based on directional plasma scald was proposed to interpret observed damage growth phenomenon.

An angle-insensitive broadband absorber of graphene covering the whole visible spectrum is numerically demonstrated, which is resulted from multiple couplings of the electric and magnetic dipole resonances in the narrow metallic grooves. This is achieved by integrating the graphene sheet with a multi-grooved metasurface separated by a polymethyl methacrylate (PMMA) spacer, and an average absorption efficiency of 71.1% can be realized in the spectral range from 450 to 800 nm. The location of the absorption peak of graphene can be tuned by the groove depth, and the bandwidth of absorption can be flexibly controlled by tailoring both the number and the depth of the groove. In addition, broadband light absorption enhancement of graphene is robust to the variations of the structure parameters, and good absorption properties can be maintained even the incident angle is increased to 60°.Electronic supplementary materialThe online version of this article (10.1186/s11671-019-2937-7) contains supplementary material, which is available to authorized users.

We proposed an analytical method to design optical minus filters by the thickness modulation of discrete, homogeneous thin-film layers of a two-material multilayer coating. The main stack provides the narrow, second-order rejection band, and the correct thickness-modulation apodization and match layers can effectively suppress the sidelobes of the passband. Using this approach, we can design minus filters with layer thicknesses close to half-wave of the rejection wavelength, making this method well suited for accurate monitoring during the deposition.

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