Jacob Schalch

A three-dimensional all-metal terahertz metamaterial perfect absorber

We present a three-dimensional terahertz metamaterial perfect absorber (MPA) that exhibits a high quality factor and is polarization insensitive. The unit cell is composed of two orthogonally oriented copper stand-up split ring resonators deposited on a copper ground plane with capacitive gaps in free space away from the substrate. Near unity (99.6%) absorption at ∼1.65 THz is experimentally obtained in excellent agreement with simulation results. The quality factor is ∼37, which is quite large for a terahertz MPA because of reduced material losses in the all-metal structure. According to simulation results, the MPA is insensitive to the polarization of the incident wave, and more than 90% absorption can be achieved for angles of incidence up to 60° for both TE and TM polarized incident THz waves.

Analysis of the thickness dependence of metamaterial absorbers at terahertz frequencies

Metamaterial absorbers typically consist of a metamaterial layer, a dielectric spacer layer, and a metallic ground plane. We have investigated the dependence of the metamaterial absorption maxima on the spacer layer thickness and the reflection coefficient of the metamaterial layer obtained in the absence of the ground plane layer. Specifically, we employ interference theory to obtain an analytical expression for the spacer thickness needed to maximize the absorption at a given frequency. The efficacy of this simple expression is experimentally verified at terahertz frequencies through detailed measurements of the absorption spectra of a series of metamaterials structures with different spacer thicknesses. Using an array of split-ring resonators (SRRs) as the metamaterial layer and SU8 as the spacer material we observe that the absorption peaks redshift as the spacer thickness is increased, in excellent agreement with our analysis. Our findings can be applied to guide metamaterial absorber designs and understand the absorption peak frequency shift of sensors based on metamaterial absorbers.

Electromechanically Tunable Metasurface Transmission Waveplate at Terahertz Frequencies

Dynamic polarization control of light is essential for numerous applications ranging from enhanced imaging to materials characterization and identification. We present a reconfigurable terahertz metasurface quarter-waveplate consisting of electromechanically actuated micro-cantilever arrays. Our anisotropic metasurface enables tunable polarization conversion cantilever actuation. Specifically, voltage-based actuation provides mode selective control of the resonance frequency, enabling real-time tuning of the polarization state of the transmitted light. The polarization tunable metasurface has been fabricated using surface micromachining and characterized using terahertz time domain spectroscopy. We observe a ~230 GHz cantilever actuated frequency shift of the resonance mode, sufficient to modulate the transmitted wave from pure circular polarization to linear polarization. Our CMOS-compatible tunable quarter-waveplate enriches the library of terahertz optical components, thereby facilitating practical applications of terahertz technologies.

An air-spacer terahertz metamaterial perfect absorber for sensing and detection applications

We designed, fabricated, and characterized a metamaterial perfect absorber at terahertz (THz) frequency range utilizing air as the dielectric material. Due to the avoidance of the loss usually introduced by the dielectric material, there was a three times improvement of the quality factor. Also, with metamaterials fabricated on a free-standing silicon nitride membrane, high sensitivity can be achieved compared with traditional metamaterials on thick substrate. Moreover, the absence of the dielectric materials presents the special opportunity to use liquid or gas as the dielectric layer for permittivity characterization or sensing and detection purposes

Terahertz metamaterial perfect absorber with continuously tunable air spacer layer

We present a comprehensive investigation of a continuously tunable metamaterial perfect absorber operating at terahertz frequencies. In particular, we investigate a three-layer absorber structure consisting of a layer of split ring resonators and a metallic ground plane, with a central layer consisting of a mechanically tunable air-spaced layer. The absorber was characterized using terahertz time-domain spectroscopy in reflection (at normal incidence) as a function of spacer thickness from 0 to 1000 μm. Our experimental measurements reveal the detailed evolution of the absorption bands as a function of spacing, in excellent agreement with analysis using interference theory and simulation. Our Fabry-Perot-like structure provides an avenue for achieving massive tunability in metamaterial absorber devices.We present a comprehensive investigation of a continuously tunable metamaterial perfect absorber operating at terahertz frequencies. In particular, we investigate a three-layer absorber structure consisting of a layer of split ring resonators and a metallic ground plane, with a central layer consisting of a mechanically tunable air-spaced layer. The absorber was characterized using terahertz time-domain spectroscopy in reflection (at normal incidence) as a function of spacer thickness from 0 to 1000 μm. Our experimental measurements reveal the detailed evolution of the absorption bands as a function of spacing, in excellent agreement with analysis using interference theory and simulation. Our Fabry-Perot-like structure provides an avenue for achieving massive tunability in metamaterial absorber devices.

A high-Q three-dimensional terahertz metamaterial perfect absorber

In this paper, we present a three-dimensional (3D) terahertz metamaterial perfect absorber (MPA) with a high quality factor. The absorption response of the proposed structure is analyzed and optimized using coupled mode theory and numerical simulations. Subsequently, we fabricate the 3D MPA by employing the multi-layer electroplating process and characterize it using terahertz time domain spectroscopy. A quality factor of 20 is verified by the experimental results, which agrees well with the simulation. The high-Q MPA has potential applications in chemical and biological sensing.