A thin film broadband absorber based on multi-sized nanoantennas

Abstract

We experimentally demonstrate an infrared broadband absorber for TM polarized light based on an array of nanostrip antennas of several different sizes. The broadband property is due to the collective effect of magnetic responses excited by these nano-antennas at distinct wavelengths. By manipulating the differences of the nanostrip widths, the measured spectra clearly validate our design for the purpose of broadening the absorption band. The present broadband absorber works very well in a wide angular range.In the last decade, plasmonic nano-antennas have experienced a drastical boom period due to their enormous capability to compress light into a subwavelength region with an extremely strong amplitude. 1,2 To date, they have found significant application in diverse areas including sensor detection, 3 solar power harvesting, 4 thermal emission, 5 biomedical imaging, 6 ultrafast modulating, 7 etc. Patterned plasmonic antennas play a significant role for the design of thin film light absorbers, which suppress both the transmission and the reflection while maximizing the absorption. The first perfect absorber that composed by metallic split ring resonators and cutting wires was demonstrated by Landy et. al. 8 Then, it was followed by some work to improve the angular and polarization performance. [9][10][11][12] Nevertheless, all of the above absorbers work at a single band frequency which limits the pragmatic applications such as THz multi-frequency spectroscopy detection. 13 By incorporating different patterns of metallic elements, two dual band absorbers were carried out by different groups. 14,15 Recently, it was reported that based on an H-shaped nano-resonator array, a dual band plasmonic metamaterial absorber could also be constructed. 16 But they are still limited to a relative narrow band response. So far, to design a thin film absorber with broadband spectrum is still quite challenge. In our group, we have made some efforts in this aspect, by stacking multiple layers of metallic crosses with different geometrical dimensions to merge several closely positioned resonant peaks in the absorption spectrum. 17 However, this proposal suffers from one crucial drawback, namely that in the fabrication it is difficult to obtain perfect alignment to match the relative position of each pattern in different layers.It is well known that a three layered structure composed by an array of plasmonic nanostrip antennas of a fixed width on top of a ground reflecting mirror and a very thin spacer layer 18 can efficiently absorb electromagnetic wave at a certain frequency. The principle of the light absorbing is that the upper strip and the ground metal layer support a pair of anti-parallel dipoles with quite closed distance in-between, the interference of those two dipoles in far field is destructive due to their π shift phase difference so that the reflection can be totally cancelled.In this letter, also aiming at broadening the absorption band, we borrow the concept of the collective effect of multiple different oscillators 1...

Enhanced broadband absorption in gold by plasmonic tapered coaxial holes

“…However, their absorption spectra are always limited due to the resonant properties [8][9][10]. Fortunately, the spectrum can be expanded when different resonators of different resonating frequencies are mixed together, e.g., by distributing different resonators in one period [11][12][13][14] or stacking multiple metal-dielectric layers [15][16][17]. Particularly in the stacked multi-layer configuration, a more expanded absorption spectrum can be obtained due to non-resonant slowlight modes induced by multiple resonances [16,17].…”

“…In the solar spectral range, resonances in the metamaterial absorbers are always modified by surface plasmon polaritons (SPPs) due to the dielectric properties of the compositional metals [2,18]. It is well-known that SPPs have a strong ability to route and manipulate photons in a subwavelength region [2,18], where photons can be strongly absorbed by the compositional metallic and/or lossy dielectric materials [3,[11][12][13][14][15][16][17]. More than one material is contained in all these absorbers, making fabrication more complex [3,[11][12][13][14][15][16][17].…”

Broadband Absorption Engineering of Hyperbolic Metafilm Patterns

“…In recent years, multiple top pattern units with different dimensions in a single period were fabricated to support different magnetic resonances and therefore broaden the absorption band of singlepaired planar meta-absorbers [41][42][43][44] . An ideal broadband absorption resonance requires an optimized selection of period and width, which is difficult to obtain due to the limited tunability of the pattern width within a given period.…”

Ultrathin Metamaterial for Polarization Independent Perfect Absorption and Band-pass Filter

“…By tuning the electric and magnetic responses and the impedance z (ω) of metamaterials, a near unity absorption peak can be realized theoretically and experimentally at the resonant frequency. Since the first reported MA, various kinds of perfect metamaterial absorbers (MAs) have been developed to achieve the goals: multiband [10][11][12][13][14][15][16][17][18], wide band [19][20][21][22][23][24], and independent of polarization and the incident angle of electromagnetic waves [14][15][16][17][18][23][24][25][26][27][28].…”