![]() ![]() In some particular cases such as the spectroscopy study and applications, enhanced (propagating) high-order diffractions which are angularly dispersive are desirable. For metasurfaces composed of small apertures, the subwavelength features will suppress the high-order modes, giving rise to enhanced zero-order diffraction in certain wavelength regions 3. In the metamaterial studies, this enables the construction of an effective medium with exotic optical properties. Up to date, most of research interests have been focused on subwavelength plasmonic system, where the lattice period is smaller or much smaller than the working wavelength 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19. The metal nanostructures such as metal-insulator-metal sandwiches can also be used to construct the electromagnetic wave absorbers 10, 11, 12, 13, 14, which may find a host of potential applications in solar cells, photodetectors, bolometers, etc. With periodic array of nanoholes or nanoparticles, enhanced optical transmission, polarization conversion, negative or high index and anomalous refraction etc. As building blocks of metasurface and metamaterial designs, isolated nanoholes in a metal or nano metal-particles in a dielectric can induce surface-plasmon polariton (SPP) mode or localized surface-plasmon (LSP) resonance 1, 2. Metal nanostructures provide great potential for manipulating light, because of the strong coupling between electromagnetic fields and surface charges. The proposed plasmonic structure is planar and ultra-thin (with an etching depth of only 80 nm), showing new potential for constructing compact and efficient dispersive elements. The zero-order reflection is suppressed, giving rise to an enhancement of first-order diffraction (50 ~ 95%) in an ultra-wide bandwidth (600 ~ 1500 nm). For the purpose, we employ symmetric or asymmetric metal patches on a ground metal plane, which support the localized oscillation of free electrons and enhanced scattering of light. Here, we show that ultra-broadband and strongly enhanced diffraction can be achieved with the super-wavelength metasurfaces. Nonetheless, much interest has been focused on the subwavelength metasurfaces working in the zero-order regime. Plasmonic materials may exhibit unprecedented ability for manipulating light. Conventionally, the dielectric gratings can be used to realize the enhanced diffraction, but the facets are usually rugged and optically thick (~μm). I.e., 3rd, 6th, 9th etc., order of the spectra will be absent corresponding to a minima due to a single slit given by m = 1, 2, 3 etc.Enhanced high-order diffractions which are spatially dispersive are desirable in such as spectroscopy studies, thin-film solar cells, etc. This is the condition for the absent spectra in the diffraction pattern If a= b i.e., the width of transparent portion is equal to the width of opaque portion then from equation (3) n = 2m i.e., 2nd, 4th, 6th etc., orders of the spectra will be absent corresponds to the minima due to single slit given by m = 1, 2, 3 etc.Therefore dividing equation (2) by equation (1) ![]() If the two conditions given by equation (2) are simultaneously satisfied then the direction in which the grating spectrum should give us a maximum every slit by itself will produce darkness in that direction and hence the most favourable phase for reinforcement will not be able to produce an illumination i.e., the resultant intensity will be zero and hence the absent spectrum. ![]() Where m = 1, 2, 3, …… excluding zero but the condition for nth order principles maximum in the grating spectrum is Thus the mining of single slit pattern are obtained in the direction given by. It happen when for again angle of diffraction 0, the path difference between the diffracted ray from the two extreme ends of one slit is equal to an integral multiple of A if the path difference between the secondary waves from the corresponding point in the two halves will be A/2 and they will can all one another effect resulting is zero intensity.
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