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

Andreas Tittl University of Stuttgart, 4th Physics Institute and Research Center SCOPE, Stuttgart, Germany Moshe G. Harats The Hebrew University of Jerusalem, The Racah Institute of Physics, Jerusalem, Israel Ramon Walter University of Stuttgart, 4th Physics Institute and Research Center SCOPE, Stuttgart, Germany Xinghui Yin University of Stuttgart, 4th Physics Institute and Research Center SCOPE, Stuttgart, Germany Martin Schäferling University of Stuttgart, 4th Physics Institute and Research Center SCOPE, Stuttgart, Germany Na Liu Max Planck Institute for Intelligent Systems, Max Planck Institute for Intelligent Systems, Stuttgart, Germany Ronen Rapaport The Hebrew University of Jerusalem, The Racah Institute of Physics, Jerusalem, Israel Harald Giessen University of Stuttgart, 4th Physics Institute and Research Center SCOPE, Stuttgart, Germany

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 [1], 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.

Disordered perfect absorber

Fig. 1 (a) - Measurement of the reflection as a function of wavelength and angle from a disordered sample. (b) SEM image of the disordered sample. (c) The impedance and the reflection obtained from a FDTD simulation. (d) A histogram of the distance between the different gold nanodisks.

[1] Tittl A., Harats M. G., Walter R., Yin X., Schäferling M., Liu N., Rapaport R., Giessen H., ACS Nano, 2014, 8 (10), pp 10885-10892

moshe.harats@mail.huji.ac.il