Design And Analysis Of DAST-Based Metamaterials

In the past decades, studies on metamaterials encompass numerous amazing topics, ranging from microwave to visible light, from fundamental research to applications. Particularly, new progresses in nonlinear metamaterials, metamaterials with gain, actively tunable metamaterials, transformation optics and quantum metamaterials provide not only the foundation for the development of ground-breaking photonic devices, but also a rich nutrient medium for systematic studies of fundamental physical effects. On the other hand, 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate(DAST) is a very important organic material which specially exhibits pronounced birefringence effect, transverse optical phonon, electro-optic effect and second-order nonlinear effect, holding great potential for applications in terahertz emitting and detecting, as well as high-speed electro-optic modulation, electro-optical sampling and integrated optical waveguide.In this thesis, we present a rich set of novel optical phenomena by incorporating DAST into metamaterials as a part of the structure serving as a dielectric layer. The main results of our work are listed as follows:(1) Simulations were performed and a polarization dependent resonant absorption over 29% in bandwidth, from 1.54 THz to 2.07 THz, in our designed DAST based metamaterials was realized by using the large birefringence effect of DAST.(2) Single-crystal DAST exhibits a strong resonant absorption peak at 1.1THz, due to the transverse optical phonon. By incorporating the resonance of DAST and metamaterial structure into a coupled system, simulations were performed and we demonstrated that the coupling between DAST molecule and metamaterial structure, as known as light-matter coupling, belongs to strong Rabi splitting with Rabi frequency 2ΩR/2π=0.37 THz. The value of 0.37 THz is already a significant fraction, 31% of the eigen-frequency 1.1THz. Simulations were also performed with a set of resonant structure sizes, the positions of splitting frequency show a good agreement with theoretical predictions.(3) Polycrystalline DAST-based metamaterials were designed and successfully fabricated. The measurements showed that the as-designed metamaterials exhibit an absorption peak at 1.04 THz as large as 50% in magnitude. Moreover, if a patterned SiO2 layer is pre-deposited on the ground Al plane, a significant improvement in absorption, reaching 60%, is achieved in the polycrystalline DAST-based metamaterials, attributing to the induced patterned SiO2 layer, which plays a positive role in the growth of smooth and less fluctuated DAST films.(4) In addition, we experimentally observed hybridization induced transparency in the as-fabricated polycrystalline DAST-based metamaterials, stem from the weak coupling between DAST molecule vibration and F-P subwavelength cavity resonance of the metal-dielectric-metal structure.(5) Furthermore, single-crystal DAST-based metamaterials were designed and successfully fabricated for the first time. In such novel single-crystal DAST-based metamaterials, we experimentally observed strong coupling between DAST crystal and metamaterial structure, as well as polarization dependent responses, all of which are originated from the intrinsic anisotropy and transverse optical phonon of DAST crystal.We believe that these valuable results reported in this dissertation would not only bring new inspiration to the applications of DAST, but also extend the regime of metamaterials. Particularly, the coupling between DAST and metamaterials provides a good example for the experimental realization of the fundamental physical effects related to light-matter coupling.