Investigation Of Negative Refraction And Goos-H(?)nchen Effect In Chiral Metamaterials

Metamaterials are engineered composites that exhibit superior properties not observed in the constituent materials or nature. By the design of order structure in certain key physical scale, metamaterials can break through the limitation of apparent nature rule and obtain exceptional material functions. It is no doubt that the advent of metamaterials will provide new opportunities to the design and fabricating of new materials. Up till now, a few metamaterials have been developed, including left-handed materials, electromagnetic stealth materials and chiral metamaterials. The emergence of metamaterials is closely related to the left-handed materials. When the electromagnetic waves propagate in left-handed materials, the electrical field ( E ), the magnetic field ( H ) and the wave vector ( k ) satisfy the"left-handed"rule and the refraction is negative, so left-handed materials are also called negative refraction materials. Recently, left-handed materials have attracted a great deal of attention within the scientific community due to their special potential applications, such as waveguide, perfect lens, the atenna, the transparency of the electromagnetic waves and so on. Furthermore, since chiral material has novel structural features and electromagnetic properties, the negative refraction in the chiral material has been widely studied by many researchers. Using chiral materials, one could realize negative refraction in optical region without making artificial magnetic materials or requiring permittivity-permeability resonance(s) in that frequency range. At this point, the artificial chiral metamaterial seems to be a good candidate to achieve the negative refraction and has become a research hotspot.In this thesis, we propose an artificial chiral composite structure which can obtain negative refraction, and then we focus on the reflection and refraction properties of electromagnetic wave in chiral metamaterial and investigate the Goos-Hanchen effect associated with the chiral metamaterial. The thesis is organized as follows:I. Negative refraction in chiral composite materialsAssuming the chiral composite materials are formed by a dilute concentration of electrically small chiral spheres in a homogeneous achiral host medium, we adopt the extended Maxwell-Garnett approximation to study the effective permittivity, the effective permeability, the effective chirality and refraction index. Theoretical results show that there exists negative refraction in high (or low) frequency region for right- (or left-) circular polarized wave, and the region is widened for large volume fraction and small damping factor. In addition, the magnitude of negative refractive index increases with decreasing the dielectric loss. Moreover, it is numerically shown that the negative refraction results from relatively large chirality parameter in chiral composites compared to the corresponding parameters in the components.II. Goos-Hanchen shift at the surface of chiral metamaterialWe theoretically analyze transmission properties of electromagnetic waves in chiral medium and investigate the Goos-Hanchen shift at the surface of chiral metamaterial. When a linearly polarized wave is incident onto the chiral medium from normal material, it splits into two transmitted waves (one is right-circular polarized (RCP) and the other is left-circular polarized (LCP)) propagating into the chiral medium and a reflected wave with both parallel and perpendicular components propagating back into the dielectric. Then there exists two critical angles: smaller critical angle corresponding to LCP wave and larger critical angle corresponding to RCP wave. Based on Artmann's formula, we mainly discuss the Goos-Hanchen shift at the interface of the chiral metamaterial, and compare it with the conventional chiral material. It is found numerically that positive and negative shifts can be attained when the incident angle is greater than the smaller critical angle, whereas if the incident angle exceeds the larger critical angle, only positive shifts can be observed for both two components. These results are opposite to those from the normal chiral materials. Furthermore, a Gaussian beam is adopted to illustrate the effect of the Goos- Hanchen shifts.III. Goos-Hanchen shift of an electromagnetic wave reflected from a slab of chiral metamaterialOn the basis of the discussion about the Goos-Hanchen shift at the surface of the chiral metamaterial, we further study the Goos-Hanchen shifts of an electromagnetic wave reflected from a slab of chiral metamaterial. Combined with the reflection and transmission characteristics in chiral medium, we calculate the Goos-Hanchen shifts of the reflected waves from a negative chiral slab based on Artmann's formula. Numerical results show that Goos-Hanchen shifts for both parallel and perpendicular reflected components can be greatly enhanced near the pseudo-Brewster angle of the reflection coefficient. In addition, we predict that Goos-Hanchen shifts depend not only on the slab thickness, but also on the incident angle. In particular, when the incident angle is close to the critical angle of total reflection for LCP wave, the Goos-Hanchen shifts of both reflected components oscillate with respect to the thickness of the slab, and its overall tendency is increasing along with the slab thickness.