Propagation characteristics of transverse electromagnetic waves in a finite-size metallic superlattice of two alternating Al–Mg layers

Abstract

Transfer matrix method has been used to investigate the propagation characteristics of a finite-size metallic superlattice. Wave reflectance, absorbance, and transmittance have been obtained for normally incident electromagnetic wave on a finite-size superlattice of two alternate layers of Aluminum and Magnesium. Such a periodic medium represents a simple model for a one dimensional photonic crystal. At low wave frequencies, the incident wave energy is shared between reflection and absorption with negligible transmission. Numerical calculations show a perfect absorption band for high number of unit cells N (above 100), which degrades as N decreases. The absorbance curves are interrupted by dips whose positions coincide with peaks in the reflectance curves along the wave energy axis. The reflectance profile revealed missing orders of reflection depending on the geometry of the superlattice. This is attributed to the excitation of interface plasmon modes that scatter incident radiation with wave vectors violating the Laue condition of diffraction. The reflectance is found to be well characterized by a finite number of unit cells for all wave energies. With increasing wave energy, the reflectance and the absorbance decrease and the superlattice becomes transparent in the high frequency range. Generally, the transmittance and absorbance characteristics of the superlattice were found to be strongly dependent on the number of unit cells of the superlattice under consideration. It has also been found that at high wave energies the superlattice becomes transparent; the real part of the input impedance approaches the vacuum impedance Z0 ​= ​377 ​Ω, while its reactance tends to zero.