- The paper presents a multiplexed plasmonic design that achieves near-perfect absorption (>98%) over a broad MWIR band.
- It employs dual-sized gold squares on a MgF₂ spacer to activate two distinct surface plasmon-polariton resonances.
- Empirical measurements and FDTD simulations indicate promising applications in optical sensing, imaging, and energy harvesting.
This paper presents a detailed investigation and experimental demonstration of a wide-band perfect light absorber operating in the mid-wave infrared (MWIR) range, employing multiplexed plasmonic metal structures. Through the implementation of different size gold metal squares multiplexed within each unit cell of a layered metamaterial structure, the authors achieve near-perfect light absorption over an expanded spectral band compared to traditional non-multiplexed absorbers.
Methodology and Experimental Setup
The core principle underpinning the absorption mechanism in this paper is the excitation of surface plasmon-polaritons (SPPs), which contribute to the anomalous absorption characteristics observed in structured metals. The research leverages two different-sized gold squares multiplexed on a thin magnesium fluoride (MgF₂) dielectric spacer supported on a thick gold substrate. This design takes advantage of two distinct surface plasmon resonance modes, thus broadening the absorption band.
The authors utilized finite-difference time-domain simulations, applying a Lorentz-Drude material model, to optimize the geometrical parameters ensuring minimal power reflection. The periodic configurations of gold squares were lithographically patterned on a sub-micrometer scale to create both non-multiplexed and multiplexed absorbers.
Results and Observations
The results, corroborated by both numerical simulations and empirical measurements, demonstrate that the multiplexed absorber structure realizes higher efficiency. Specifically, the power reflectivity data for the multiplexed configuration shows above 98% absorption over the MWIR wide spectral band, centered around a wavelength of 3.45 µm. This is in stark contrast to the narrower absorption bands seen in non-multiplexed structures, which exhibit peak absorption at narrowed widths (3.347 µm and 3.525 µm for different unit cell sizes), with reflectivity at specific wavelengths as low as 0.16% and 0.06%, respectively.
Electromagnetic field distribution studies reveal that the strong local field enhancements in different portions of the multiplexed structure account for this expanded absorption band. Resonant excitations vary depending on the wavelength, as different sized metal squares interact in distinct manners within the MgF₂ spacer layer.
Implications and Future Prospects
The implications of such enhanced broadband absorption in the MWIR region are significant for technological applications involving enhanced optical signal sensing and imaging. The two-resonance mode system employed here indicates potential for further developments in adaptive photodetectors and energy-harvesting devices. Moreover, the fine-tuning of geometric parameters and material properties could lead to tailored absorption across specified infrared bands, optimizing performance for diverse scientific and industrial applications.
The paper suggests future avenues for exploring other multiplexed configurations involving different plasmonic materials or hybrid metamaterial structures for optimized photonic and thermal management applications. As the field advances, there may be opportunities to apply multiplexed plasmonic absorbers in dynamic and flexible photonic systems, potentially enabling tunable responses to variable environmental stimuli.
This research exemplifies the intricate interplay between structural engineering at nanoscale dimensions and the optical properties of materials, charting a pathway for enhancing functional capabilities in photonic devices.