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Novel Terahertz Metamaterials

Dr. Antoinette J. Taylor, Los Alamos National Laboratory

Monday, November 18, 2013
3:00 p.m.–4:30 p.m.
Sloan Auditorium

Abstract:
Electromagnetic metamaterials are structured composites with patterned metallic sub-wavelength inclusions. These mesoscopic systems are built from the “bottom up”, at the unit cell level, to yield specific electromagnetic properties. Individual components respond resonantly to the electric, magnetic, or both components of the electromagnetic field. In this way electromagnetic metamaterials can be designed to yield a desired response at frequencies from the microwave through the visible. Importantly, additional design flexibility is afforded by the judicious incorporation of naturally occurring materials within the active region of the metamaterial elements. Specifically, hybrid metamaterial composites result when the properties of a natural material, e.g. semiconductors or complex oxides strongly couple with the resonance of a metamaterial element. The resulting hybrid metamaterials will still exhibit “passive” properties (e.g. negative electric response, negative index, gradient index, etc.), as determined by the patterning of the metamaterial elements. However, the aforementioned coupling engenders control of the passive metamaterial response via external stimulus of the natural material response (photoconductivity, nonlinearity, gain, etc.).

In recent years terahertz (1 THz = 1012 Hz) technology has become an optimistic candidate for numerous sensing, imaging, and diagnostic applications. Nevertheless, THz technology still suffers from a deficiency in high-power sources, efficient detectors, and other functional devices ubiquitous in neighboring microwave and infrared frequency bands, such as amplifiers, modulators, and switches. One of the greatest obstacles in this progress is the lack of materials that naturally respond well to THz radiation. The potential of metamaterials for THz applications originates from their resonant electromagnetic response, which significantly enhances their interaction with THz radiation. Thus, metamaterials offer a route towards helping to fill the so-called “THz gap”.

Here, I will present metamaterials with designed novel and/or active functionality, enabling control and tuning of the amplitude, frequency and polarization state at THz frequencies1-10. In many of these materials the critical dependence of the resonant response on the supporting substrate and/or the fabricated structure enables the creation of active THz metamaterial devices. We show that the resonant response can be controlled using optical or electrical excitation and thermal tuning, enabling efficient THz devices that will be of importance for advancing numerous real-world THz applications.