Research Of Negative Refraction Metarials At The Frequency Of Visible Light

Negative refraction is a kind of novel electromagnetism phenomenon. In visible optical frequencies, the propagation paths of refractive wave and incident wave are at the same side of the normal of the interface. A flat lens made of negative refraction materials (NRM) can focus light and the resolution of the image can be smaller than the diffraction limit. NRM also can be used in invisible cloak devices which qualify NRM significance in future military. Besides, NRM bring out plenty of potential applications in visible optical frequencies, such as phase compensation, nano waveguide and so on. The research of NRM in optical frequencies has become one of the most hottest fields in decade.The artificial NRM composed of metallic wires arrays and metallic slit rings arrays was firstly detected experimentally at microwave range by D. R. Smith et al. in2000. Up to now, fishnet metamaterial has realized negative refraction at780nm. However, because of the sophistication of the cells, the NRMs are facing the challenge of the nano processing technology. Negetive refraction at660nm was obtained by silver nanowire arrays with the diameter of60nm by X. Zhang et al. in2008, but the experiment shows that the transmission is only4%/4.5μm.The microscopic mechanism of the reaction of the silver nanoline to electromagnetic wave is studied deeply, and the skin depth is about20nm. First, silver nanospheres dispersed in liquid crystals is proposed to realize negative refraction at visible optical wavelength. Silver nanospheres with the diameter of 20nm dispersed in liquid crystals are proposed to realize negative refraction at visible optical wavelength. It demonstrates that negative refraction at visible optical wavelength can be realized when the distance between the silver nanospheres is smaller than40nm. The theory turns out that the bigger the An of the liquid crystals,the wider wavelength band of negative refraction. The negative refraction band of E7liquid crystals (An=0.22)/silver nanospheres composite material is460nm-485nm. Silver nanospheres/Liquid crystals composite materials are prepared in experiment. But the device confronts with the problem of stability due to the easy reunion of the nanospheres.The distance of the silver nanowire arrys with diameter of20nm should be smaller than70nm for negative refraction at visible optical wavelength. The Ag/PA material with nanoline radius of20nm and the distance between adjacent lines of110nm is prepared by elecrodeposite. The reflection test shows the negative permittivity is-2.33for the wave with the wavelength of780nm, which proves Ag/PA is a kind of negative refraction materials. In order to improving the transmission, silver nanowires arrays with diameter of20nm and distance of40nm which are based on on reverse hexagonal lyotropic liquid crystal template is proposed. Theoretical calculation shows the nagative refraction waveband is450nm-800nm. Theory turns out the transmission is about30%beyond500nm, which means the multiple enhancement of transmittance.The conjugate π electrons in liquid crystal molecule are delocalized in applied electromagnetic fields and the dipole is induced to react to the electromagnetic fields. Liquid crystals (LC) are nearly transparent for visible optical light so the NIM based on LC has the advantage of high transmittance. Experiments turns out the max negative refraction angle can be obtained when the angle between the long aix of the molecule and electric fields is about50°. Besides, the biggest negative refraction angle is akin to in linear relation with An of LC. TM wave with wavelength of532nm can realize negative refraction in LC and the negative refraction angle is about-14°or the LC with△n=0.42, which is twice of the value reported. This work investigates the plasma of metal and dipole of the molecule and these oscillation plasmon are qualitative designed to realize negative refraction. The theoretical models of permittivity are used to predict negative refraction effect in the designed materials. All-angle negative refraction material covering almost the whole visible light is explored in this work. Meanwhile, the relation between energy loss and the specific surface area is analyzed, which turns out the radius of nanolines should be decreased to10nm to obtain valuable NRM. Though the free plasma of metal can affect electromagnetic wave strongly and change its direction of propagation, the energy loss is hard to avoid. The like-plasma of liquid crystal can’t realize all-angle negative refraction, but it has the advantage of lossless. There is still hope to solve this problem by controlling the orientation form of liquid crystal molecule, which is one of our works in future.