Quantitative Angle-Resolved Small-Spot Reflectance Measurements on Plasmonic Perfect Absorbers: Impedance Matching and Disorder Effects

Abstract

Plasmonic devices with absorbance close to unity have emerged as essential building blocks for a multitude of technological applications ranging from trace gas detection to infrared imaging. A crucial requirement for such elements is the angle independence of the absorptive performance. In this work, we develop theoretically and verify experimentally a quantitative model for the angular behavior of plasmonic perfect absorber structures based on an optical impedance matching picture. To achieve this, we utilize a simple and elegant k-space measurement technique to record quantitative angle-resolved reflectance measurements on various perfect absorber structures. Particularly, this method allows quantitative reflectance measurements on samples where only small areas have been nanostructured, for example, by electron-beam lithography. Combining these results with extensive numerical modeling, we find that matching of both the real and imaginary parts of the optical impedance is crucial to obtain perfect absorption over a large angular range. Furthermore, we successfully apply our model to the angular dispersion of perfect absorber geometries with disordered plasmonic elements as a favorable alternative to current array-based designs.

Numerical study of a wide-angle polarization-independent ultra-broadband efficient selective metamaterial absorber for near-ideal solar thermal energy conversion

“…The average absorption can reach as high as 98.95% over the wavelength range of 260 to 1580 nm, which signicantly exceed most of previously reported metamaterial solar absorbers both in the efficiency and bandwidth of solar absorption. 6,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] The proposed solar absorber are numerically demonstrated to possess a near perfect absorption in the UV region from 250 to 400 nm. At the same time, the mid-infrared absorption is decreased signicantly, which is remarkably benecial for the improvement of the total photothermal conversion efficiency.…”

“…Yet recent demonstrations show that it can be harnessed using mechanisms such as multiple resonances, impedance matching, and slow-light modes to create broadband absorption. [25][26][27][28][29][30][31][32][33][34][35][36][37] Particularly, the metamaterial nanostructures by utilizing metal/dielectric stacks are the most widely used way to realize broadband high absorption at present, which are explained by slow light characteristics in the multi-layer metal/dielectric stack. [25][26][27][28][29][30][31][32][33][34][35][36][37] These metal/dielectric multilayer structures are proposed as one kind of hyperbolic metamaterial (HMM).…”

“…[25][26][27][28][29][30][31][32][33][34][35][36][37] Particularly, the metamaterial nanostructures by utilizing metal/dielectric stacks are the most widely used way to realize broadband high absorption at present, which are explained by slow light characteristics in the multi-layer metal/dielectric stack. [25][26][27][28][29][30][31][32][33][34][35][36][37] These metal/dielectric multilayer structures are proposed as one kind of hyperbolic metamaterial (HMM). For example, Cui et al numerically presented a broadband saw-toothed infrared absorber made of alternating layers of gold and germanium layers, which realize an absorption over 95% in the wavelength ranging from 3 to 5.5 mm; 25 Liang et al numerically demonstrated a two-dimensional ultra-broadband pyramid absorber having a high absorption performance at the range of 1-14 mm, which is based on the metamaterial structure utilizing 15 gold/Ge pairs; 30 Lin et al theoretically investigated a nano-cone array formed by alternating W and Ge thin lms, which can realize an average absorption approaching 98% in the wavelength range of 0.3-9 mm; 34 Obviously, while realizing broadband operating ranges in these studies, the poor selectivity of absorption spectra is a serious drawback of these tapered multilayered absorbers for solar energy harvesting.…”

A Large‐Area, Mushroom‐Capped Plasmonic Perfect Absorber: Refractive Index Sensing and Fabry–Perot Cavity Mechanism

“…The mechanism of MPA has been explained through a number of models including impedance matching [ 17,21,33 ] and destructive interference. [ 34 ] In the impedance matching mechanism, the entire three-layered structure is considered as a homogeneous medium.…”

“…[ 34 ] In the impedance matching mechanism, the entire three-layered structure is considered as a homogeneous medium. At the perfect absorbing wavelength, the effective permittivity and the effective permeability reach the same value, ε μ = eff eff , so that the impedance (both the real part and the imaginary part [ 33 ] ) matches to the free space, 1…”