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°.

Broadband metamaterial absorbers (MAs) are critical for applications of photonic and optoelectronic devices. Despite long-standing efforts on broadband MAs, it has been challenging to achieve ultrabroadband absorption with high absorptivity and omnidirectional characteristics within a comparatively simple and low-cost architecture. Here we design, fabricate, and characterize a novel compact Cr-based MA to achieve ultrabroadband absorption in the visible to near-infrared wavelength region. The Cr-based MA consists of Cr nanorods and Cr substrate sandwiched by three pairs of SiO₂/Cr stacks. Both simulated and experimental results show that an average absorption over 93.7% can be achieved in the range of 400–1000 nm. Specifically, the ultrabroadband features result from the co-excitations of localized surface plasmon (LSP) and propagating surface plasmon (PSP) and their synergistic absorption effects, where absorption in the shorter and longer wavelengths are mainly contributed bythe LSP and PSP modes, respectively. The Cr-based MA is very robust to variations of the geometrical parameters, and angle-and polarization-insensitive absorption can be operated well over a large range of anglesunder both transverse magnetic(TM)- and transverse electric (TE)-polarized light illumination.

Antireflection sub-wavelength structures (SWSs) on ZnS were designed and ZnS SWSs with HfO₂ protective film were prepared, and their properties in long-wave infrared applications were examined and compared to AR coatings. The SWS has good antireflection performance and exhibits less polarization sensitivity than the AR coating. At temperatures above 500 °C, the SWS with HfO₂ protective film has a better thermal endurance property than the multilayer AR coating. Moreover, the HfO₂ protective film significantly improved the mechanical properties of the ZnS SWS and was similar to HfO₂ covered AR coating when the HfO₂ film was not broken. This study shows that the ZnS SWS with HfO₂ protective film has promising application prospects in infrared optical windows.

The flagship monthly journal of SPIE, Optical Engineering (OE) publishes peer-reviewed papers reporting on research and development in all areas of optics, photonics, and imaging science and engineering.

A comparative study of laser induced damage of HfO₂/SiO₂ and TiO₂/SiO₂ mirrors at 1064 nm has been carried out. One TiO₂/SiO₂ mirror with absorption of 300 ppm and two HfO₂/SiO₂ mirrors with absorption of 40 and 4.5 ppm were fabricated using electron beam evaporation method. For r-on-1 test, all HfO₂/SiO₂ mirrors with low average absorption are above 150 J/cm² at 10ns. However, the TiO₂/SiO₂ mirrors with high average absorption are just 9.5 J/cm², which are probably due to the rather high absorption and rather low band gap energy. Meanwhile, all the samples were irradiated from front and back side respectively using the raster scan test mode. In case of front side irradiation, it is found that: for TiO₂/SiO₂ high reflectors, the representative damage morphologies are shallow pits that were probably caused by absorbing centers. However, for HfO₂/SiO₂ high reflectors, the dominant damage morphologies are micrometer-sized nodules ejected pits and the delamination initiating from the pits. The absorption of HfO₂/SiO₂ coatings is low enough to have minor influence on the laser damage resistance. In case of backside irradiation, the morphology of TiO₂/SiO₂ mirrors is mainly center melted pits that are thermal melting induced damage. Meanwhile, HfO₂/SiO₂ mirrors with isometrical fracture rings damage morphology are thermal induced stress damage.