Enhancing sensing capacity of terahertz metamaterial absorbers with a surface-relief design

Metamaterial absorbers(MAs)serve as important electromagnetic wave-absorbing devices that have captured the attention of researchers for a long term.Functioning as sensitive detectors to determine perturbations in an ambient environment is another significant subsidiary function.Here,we theoretically propose an optimized fabrication method to implement terahertz MAs with fewer steps and also evaluate both absorption and sensing performances of such MAs realized by the new method.Simulation findings demonstrate that such MAs can basically maintain the original absorption features perfectly,including near-complete absorption at resonance as well as strong robustness to wide incident angles.Specifically,the full width at half-maximum and quality factor of the absorption resonances attenuate less than 26%and 8%with this new method,remaining in the ranges of^0.03–0.04 THz and^20–27 for two selected example MAs.More significantly,sensing capacities of this type of MA,in terms of maximum detection range(enhancing at least 9%),observable spectral modulation(increasing at least 6.3%),and refractive index sensitivity,are improved to a large extent because of more intense coupling between resonant field and matter in the case of surface-relief MAs.This stronger coupling results from exposing more spots of the resonantly high field to direct contact with an approaching analyte,which is illustrated by field profiles of the MAs at resonance in this work.Additionally,other desirable absorber features are also explored with such MAs,like functioning as building blocks to configure multiband MAs and strong robustness against fabrication errors.Such new-style terahertz MAs shown in the paper,acting as good examples,not only prove that terahertz MAs can be fabricated by the proposed time-and cost-saving route in contrast to the traditional MA fabrication process,but also can serve as novel platforms to explore other intriguing terahertz photonic effects,such as the field enhancement effect.

Laser-induced controllable chirped-pitch circular surface-relief diffraction gratings on AZO glass

Chirped-pitch nanoscale circular surface-relief diffraction gratings were photoinscribed on thin films of a Disperse Red 1 functionalized material using a holographic technique. A truncated conical mirror splits and redirects a converging or diverging laser beam, resulting in an interference pattern of concentric circles with a chirped pitch that can be controlled by varying the wavefront curvature. The resulting circular gratings have a diameter of 12 mm and have the advantage of being produced in a fast, single-step procedure with no requirement for a master grating,photomask, or milling equipment.

Extraordinary Transmission through Metallic Grating with Subwavelength Slits for S-Polarization Illumination

Based on the rigorous coupled-wave analysis algorithm, we have systematically analysed the effect of the geometrical parameters of a dielectric film coated metallic grating with subwavelength slits on extraordinary optical transmission for s-polarization illumination. Results show that the dielectric film which sustains a waveguide electromagnetic mode on the top of the metallic lamellar grating can strongly enhance the transmittance, the positions of the transmission peaks are mainly determined by the period of the metallic grating, the thickness and refractive index of the dielectric film. This structure shows potential applications in excellent polarizers or polarization-isotropic devices at infrared spectral range by appropriately choosing the geometrical parameters.