Temperature-tunable lasing in negative dielectric chiral nematic liquid crystal

In this work, negative dielectric nematic liquid crystal SLC 12V620-400, chiral dopant S811, and laser dye DCM are used to prepare dye-doped chiral nematic liquid crystal laser sample. In order to investigate temperature-tunable lasing in negative dielectric chiral nematic liquid crystal, we measure the transmission and lasing spectrum of this sample. The photonic band gap （PBG） is observed to red shift with its width reducing from 71.2 nm to 40.2 nm, and its short-wavelength band edge moves 55.3 nm while the long-wavelength band edge only moves 24.9 nm. The wavelength of output laser is found to red shift from 614.4 nm at 20 ~C to 662.8 nm at 67 ~C, which is very different from the previous experimental phenomena. The refractive indices, parallel and perpendicular to the director in chiral nematic liquid crystal have different dependencies on temperature. The experiment shows that the pitch of this chiral nematic liquid crystal increases with the increase of temperature. The decrease in the PBG width, different shifts of band edges, and the red shift of laser wavelength are the results of refractive indices change and pitch thermal elongation.

Effect of Different Plasmonic Nano-Inclusion on Double Negative-Semiconductor Photonic Crystal in Visible Region:Gain Assistance and All-Angle Negative Refraction

A gain assisted double negative- Metallo-semiconductor photonic crystal （DN-MSPC） for visible light with effect of different plasmonic （Al, Ag, Au, Cu） nanorod inclusion, is presented. Negative real values of both permeability （μ） and permittivity （ε） with extremely low imaginary values for visible light is obtained by applying Coupled dipole approximation. All-Angle negative refraction is obtained by applying surface plasmon polariton excitation （SPPE） in DN-MSPC operating in a dispersion regime with anti-parallel refracted wave vector and Poynting vector. Index matched to the incident light and compensated losses due the gain assistance leads the light amplification in the designed structure. Furthermore, extremely high left-handed transmission efficiency （〉99%） is also investigated. Demonstration of near and far-field resonance patterns reveal the nano-photonic device applications potential i.e. highly directional optical nanoantenna, filter, etc.

Random lasing from dye-doped negative liquid crystals using ZnO nanoparticles as tunable scatters

This work demonstrates the realization of a lasing in scattering media,which contains dispersive solution of Zn O nanoparticles（NPs） and laser dye 4-dicyanomethylene-2-methyle-6-（p-dimethylaminostyryl）-4H-pyran（DCM） in negative liquid crystals（LCs） that was injected into a cell.The lasing intensity of the dye-doped negative LC laser can be tuned from low to high if the NPs concentration is increased.The tunability of the laser is attributable to the clusters-sensitive feature in effective refractive index of the negative LCs.Such a tunable negative liquid crystal laser can be used in the fabrication of new optical sources,optical communication,and liquid crystal laser displays.

Realization of absolute negative refraction index by a photonic crystal using anisotropic dielectric material

A method to realize absolute negative refraction index -1 with a two-dimensional （2D） photonic crystal is presented by introducing dielectric anisotropy in the photonic crystal material. The band structures of E-polarization mode and H-polarization mode can be adjusted by changing the parameters of materials. Thus the two modes with different polarizations have the same negative refraction index -1 for the same frequency. The results are demonstrated by numerical simulation based on the finite-difference time-domain （FDTD） method.

Effects of doping Fe cations on crystal structure and thermal expansion property of Yb_2Mo_3O_(12)

Crystal structures and thermal expansion properties of Yb2-xFexMo3O12（x=0.0,0.6,1.0,1.1,1.4） solid solutions have been studied by X-ray powder diffraction（XRPD） at different temperatures.Rietveld analysis of the XRPD data shows that Yb2-xFexMo3O12 solid solutions adopt orthorhombic structure and have variable thermal expansion coefficients controlled by the ratio of Yb^3＋ to Fe^3＋.Yb2Mo3O12 shows anisotropic negative thermal expansion property,induced by the reductions in average Yb-O-Mo angle and average apparent Mo2-O bond length with increasing temperatures.As more Yb^3＋ substituted by Fe^3＋,the linear thermal expansion coefficients of Yb2-xFexMo3O12 increase from negative to positive.A near-zero thermal expansion coefficient of 0.55×10^-6K^-1 for Yb0.6Fe1.4Mo3O12 is observed in the temperature range of 573-873 K.