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Abstract Enhanced and controlled light absorption, as well as field confinement in optically thin materials, are pivotal for energy‐efficient optoelectronics and nonlinear optical devices. Highly doped transparent conducting oxide (TCO) thin films can support the so‐called epsilon near zero (ENZ) modes in a frequency region of near‐zero permittivity, which can lead to the perfect light absorption and ultrastrong electric field intensity enhancement (FIE) within the films. To achieve full control over absorption and FIE, one must be able to tune the ENZ material properties as well as the film thickness. Here, engineered absorption and FIE are experimentally demonstrated in aluminum‐doped zinc oxide (AZO) thin films via control of their ENZ wavelengths, optical losses, and film thicknesses, tuned by adjusting the atomic layer deposition (ALD) parameters such as dopant ratio, deposition temperature, and the number of macrocycles. It is also demonstrated that under ENZ mode excitation, though the absorption and FIE are inherently related, the film thickness required for observing maximum absorption differs significantly from that for maximum FIE. This study on engineering ENZ material properties by optimizing the ALD process will be beneficial for the design and development of next‐generation tailorable photonic devices based on flat, zero‐index optics.
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Complex analytic dependence on the dielectric permittivity in ENZ materials: The photonic doping example
Abstract Motivated by the physics literature on “photonic doping” of scatterers made from “epsilon‐near‐zero” (ENZ) materials, we consider how the scattering of time‐harmonic TM electromagnetic waves by a cylindrical ENZ region is affected by the presence of a “dopant” in which the dielectric permittivity is not near zero. Mathematically, this reduces to analysis of a 2D Helmholtz equation with a piecewise‐constant, complex valued coefficientathat is nearly infinite (say with ) in . We show (under suitable hypotheses) that the solutionudepends analytically on δ near 0, and we give a simple PDE characterization of the terms in its Taylor expansion. For the application to photonic doping, it is the leading‐order corrections in δ that are most interesting: they explain why photonic doping is only mildly affected by the presence of losses, and why it is seen even at frequencies where the dielectric permittivity is merely small. Equally important: our results include a PDE characterization of the leading‐order electric field in the ENZ region as , whereas the existing literature on photonic doping provides only the leading‐order magnetic field.
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- Award ID(s):
- 2009746
- PAR ID:
- 10478659
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Communications on Pure and Applied Mathematics
- Volume:
- 77
- Issue:
- 2
- ISSN:
- 0010-3640
- Format(s):
- Medium: X Size: p. 1278-1301
- Size(s):
- p. 1278-1301
- Sponsoring Org:
- National Science Foundation
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