Formation of ZnGa_2O_4 films by multilayer deposition and subsequent thermal annealing

The Ga203/ZnO multilayer films are deposited on quartz substrates by magnetron sputtering, the thickness values of Ga203 layers are in a range of 19 nm-2.5 nm and the thickness of ZnO layer is a constant of 1 nm. Formation of spinel ZnGa204 film is achieved via the annealing of the Ga203/ZnO multilayer film. The influences of original Ga203 sublayer thickness on the optical and structural properties of Ga203/ZnO multilayer films and annealed films are studied. With the decrease of the thickness of Ga203 sublayer, the optical band-gap of Ga203/ZnO multilayer film decreases, the intensity of UV emission diminishes and the intensity of violet emission increases. The annealed film displays the enlarged optical band gap and the quenched violet emission. UV fluorescence bands are observed from Ga203 and ZnGa204.     

Atomic NOON state generation in distant cavities by virtual excitations

A general scheme of generating NOON states of virtually-excited 2N atoms is proposed. The two cavities are fibre-connected with N atoms in each cavity. Although we focus on the case of N = 2, the system can be extended to a few atoms with N 〉2. It is found that all 2N atoms can be entangled in the form of NOON states if the atoms in the first cavity are initially in the excited states and atoms in the second cavity are all in the ground states. The feasibility of the scheme is carefully discussed, it shows that the NOON state with a few atoms can be generated with good fidelity and the scheme is feasible in experiment.     

Unidirectional emissions from dielectric photonic circuits decorated with plasmonic phased antenna arrays

Thanks to resonant characteristics of metallic nanoparticles, optical waves scattered from plasmonic nanoantennae can be well tailored in both amplitude and phase. We numerically demonstrate that, by varying the lengths and the lateral positions of gold nanorods in vicinity of a silicon waveguide, unidirectional emissions with typical forward-backward contrast ratio of 15 dB and directivity of 12 dB can be acquired in a plasmonic phased antenna array with sub-wavelength device length. The properties, i.e., the emission directionality and the size compactness, can be employed to control the far-field radiation pattern from a dielectric photonic circuit. Moreover, by altering the orientations of the dielectric waveguides decorated with plasmonic phased antenna arrays, we propose wireless light transportations in a layered photonic infrastructure, which may have applications in high-density photonic integrations.     

Sixteen-element Ge-on-SOI PIN photo-detector arrays for parallel optical interconnects

We describe the structure and testing of one-dimensional array parallel-optics photo-detectors with 16 photodiodes of which each diode operates up to 8 Gb/s. The single element is vertical and top illuminated 30μm-diameter silicon on insulator （Ge-on-SOI） PIN photodetector. High-quality Ge absorption layer is epitaxially grown on SO1 substrate by the ultra-high vacuum chemical vapor deposition （UHV-CVD）. The photodiode exhibits a good responsivity of 0.20 A/W at a wavelength of 1550 nm. The dark current is as low as 0.36/aA at a reverse bias of 1 V, and the corresponding current density is about 51 mA/cm2. The detector with a diameter of 30 t.trn is measured at an incident light of 1.55 μm and 0.5 mW, and the 3-dB bandwidth is 7.39 GHz without bias and 13.9 GHz at a reverse bias of 3 V. The 16 devices show a good consistency.     

CDCC Approaches and Roles of Closed Channels in d-Nucleus Reactions

The effect of deuteron breakup in d-nucleus reaction is treated with the continuum discretized coupled channels （CDCC） approach, and the effects on the total reaction cross sections and elastic scattering angular distributions are studied by comparing the calculations of CDCC and spherical optical model with our global deuteron optical potential [Phys. Rev. C 73 （2006） 054605] below 200 MeV, for target nuclei ranging from ^12C to ^208Pb. The contributions from the closed channels to the total reaction and breakup cross sections, and angular distributions of elastic scattering are also seriously discussed.     

Experiments on trapping ytterbium atoms in optical lattices

Experiments on trapping ytterbium atoms in various optical lattices are presented. After the two-stage cooling, first in a blue magneto-optical trap and then in a green magneto-optical trap, the ultracold 171 Yb atoms are successfully loaded into one-, two-, and three-dimensional optical lattices operating at the Stark-free wavelength, respectively. The temperature, number, and lifetime of cold 171 Yb atoms in one-dimensional lattice are measured. After optimization, the one-dimensional lattice with cold 171Yb atoms is used for developing an ytterbium optical clock.     

First-principles study of the structural,elastic, and optical properties for Sr0.5Ca0.5TiO3

A detailed theoretical study of the structural, elastic, and optical properties for Sr0.5Ca0.5TiO3 is carried out by first- principles calculations. The band structure exhibits a direct bandgap of 2.08 eV at the F point in the Brillouin zone. The bulk modulus, shear modulus, Young＇s modulus, and Poisson＇s ratio are derived based on the calculated elastic constants. The bulk modulus B = 153 GPa and shear modulus G = 81GPa are in good agreement with available experimental data. Poisson＇s ratio v = 0.275 suggests that Sr0.sCa0.sTiO3 should be classified as being a ductile material. Using the electronic band structure and density of states, we analyze the interband contribution to the optical properties. The real and imaginary parts of the dielectric function, as well as the optical properties such as the optical absorption coefficient, refractive index, extinction coefficient, and energy-loss spectrum are calculated. The static dielectric constant ε1 （0） and the refractive index n（0） are also investigated.     

N vacancy,substitutional O,and AI defects in the bandgap of composition-tunable nonstoichiometric AIN powder

AlN powders are prepared by direct nitridation via Al liquid and vapor phases in mixed atmospheres of N2 and NH3 with different NH3/N2 ratios. The reaction analysis reveals that NH3 acts as catalyst for N2 dissociation and the transportations of N, O, and Al in the liquid phase are different from those in the vapor phase. Accordingly, the products are Al-rich and composition-tunable nonstoichiometric AlN in which N, O, and Al content values change with nitridation atmosphere and temperature, leading to the variation of the relevant defect concentration. Therefore, the AlN powders exhibit prominent absorption bands around 5.30, 3.40, and 1.50 eV, which are tentatively assigned to VN, ON donors, and AlN acceptor respectively. Furthermore, a new donor named [VN-ON] complex is predicted at 4.40 eV within the 5.90 eV bandgap. It is demonstrated that the optical spectra of nonstoichiometric AlN are preferable to the nominal stoichimometric one for the identification of the defects energy level.     

Influences of anionic and cationic dopants on the morphology and optical properties of PbS nanostructures

Selenium and zinc are used as anionic and cationic dopant elements to dope PbS nanostructures. The undoped and doped PbS nanostructures are grown using a thermal evaporation method. Scanning electron microscopy （SEM） results show similar morphologies for the undoped and doped PbS nanostructures. X-ray diffraction （XRD） patterns of three sets of the nanostructures indicate that these nanostructures each have a PbS structure with a cubic phase. Evidence of dopant incorporation is demonstrated by X-ray photoelectron spectroscopy （XPS）. Raman spectra of the synthesized samples con- firm the XRD results and indicate five Raman active modes, which relate to the PbS cubic phase for all the nanostructures. Room temperature photoluminescence （PL） and UV-Vis spectrometers are used to study optical properties of the undoped and doped PbS nanostructures. Optical characterization shows that emission and absorption peaks are in the infrared （IR） region of the electromagnetic spectrum for all PbS nanostructures. In addition, the optical studies of the doped PbS nanos- tructures reveal that the band gap of the Se-doped PbS is smaller, and the band gap of the Zn-doped PbS is bigger than the band gap of the undoped PbS nanostructures.     

Rational doping for zinc oxide and its influences on morphology and optical properties

Zinc oxide(ZnO) nanopowders doped with different metal ions(Me, Me = Sn4+, In3+, Mn2+, and Co2+) are prepared by a simple sol–gel method. Influences of the ion doping on morphology and optical properties of the resulting ZnxMeyO are investigated by scanning electron microscopy, X-ray diffraction, UV-vis absorption spectrum, and photoluminescence. The morphology of ZnO can be tailored by ion doping, which is closely related not only to the ionic radii and electronegativities of the doped ions, but also to their oxidation states and electron configurations. The optical band gap and photoluminescence of ZnO can also be modulated by ion doping, which results from a combination of different effects, Burstein–Moss, band tail, charge compensation, sp–d exchange, non-radiative recombination, and blocking barrier. This may offer us a viable approach to tuning the(optical) properties of ZnO-based materials via rational ion doping.     

Structural, electronic, and optical properties of ZnOl_xSex alloys using first-principles calculations

The structural, electronic, and optical properties of binary ZnO, ZnSe compounds, and their ternary ZnOl_xSex alloys are computed using the accurate full potential linearized augmented plane wave plus local orbital （FP-LAPW ＋ lo） method in the rocksalt （B 1） and zincblende （B3） crystallographic phases. The electronic band structures, fundamental energy band gaps, and densities of states for ZnO1_xSex are evaluated in the range 0 〈 x 〈 1 using Wu-Cohen （WC） generalized gradient approximation （GGA） for the exchange-correlation potential. Our calculated results of lattice parameters and bulk modulus reveal a nonlinear variation for pseudo-binary and their ternary alloys in both phases and show a considerable deviation from Vegard＇s law. It is observed that the predicted lattice parameter and bulk modulus are in good agreement with the available experimental and theoretical data. We establish that the composition dependence of band gap is semi-metallic in B1 phase, while a direct band gap is observed in B3 phase. The calculated density of states is described by taking into account the contribution of Zn 3d, O 2p, and Se 4s, and the optical properties are studied in terms of dielectric functions, refractive index, reflectivity, and energy loss function for the B3 phase and are compared with the available experimental data.     

Realization of Tip Tilting By 8-Step Line Tilting

By direct calculation of rotation matrices of SO（3）, we show how certain specific sequence of eight consecutive rotations of digital angles can yield a tilting of a facet mirror. We also design a detailed program specifically to tilt an array of mirrors from planar orientation to the required focusing orientation. We describe how to use the 8-step to realize the focusing of the mirror array. We have found, in our designed program, an important feature of row-sharing during the rotations for the columns and similarly the column-sharing during the rotations for the row. This feature can save a lot of operating time during the actual realization of the mechanical movements.     

First-principles study of structural,electronic and optical properties of ZnF_2

The structural, electronic, and optical properties of rutile-, CaC12-, and PdF2-ZnF2 are calculated by the plane-wave pseudopotential method within the density functional theory. The calculated equilibrium lattice constants are in reasonable agreement with the available experimental and other calculated results. The band structures show that the rutile-, CaCl2-, and PdF2-ZnF2 are all direct band insulator. The band gaps are 3.63, 3.62, and 3.36 eV, respectively. The contribution of the different bands was analyzed by the density of states. The Mulliken population analysis is performed. A mixture of covalent and weak ionic chemical bonding exists in ZnF2. Furthermore, in order to understand the optical properties of ZnF2, the dielectric function, absorption coefficient, refractive index, electronic energy loss spectroscopy, and optical reflectivity are also performed in the energy range from 0 to 30 eV. It is found that the main absorption parts locate in the UV region for ZnF2. This is the first quantitative theoretical prediction of the electronic and optical properties of ZnF2 compound, and it still awaits experimental confirmation.     

Thickness dependence of the optical constants of oxidized copper thin films based on ellipsometry and transmittance

Thin oxidized copper films in various thickness values are deposited onto quartz glass substrates by electron beam evaporation. The ellipsometry parameters and transmittance in a wavelength range of 300 nm–1000 nm are collected by a spectroscopic ellipsometer and a spectrophotometer respectively. The effective thickness and optical constants, i.e.,refractive index n and extinction coefficient k, are accurately determined by using newly developed ellipsometry combined with transmittance iteration method. It is found that the effective thickness determined by this method is close to the physical thickness and has obvious difference from the mass thickness for very thin film due to variable density of film.Furthermore, the thickness dependence of optical constants of thin oxidized Cu films is analyzed.     

Increasing the rewriting e-paper by selecting speed of optical rewritable proper liquid crystals

The effect of interaction between liquid crystal （LC） and photoalignment material on the speed of optical rewriting process is investigated. The theoretical analysis shows that a smaller frank elastic constant K22 of liquid crystal corresponds to a larger twist angle, which gives rise to a larger rewriting speed. Six different LC cells with the same boundary conditions （one substrate is covered with rubbed polyimide （PI） and the other with photo sensitive rewritable sulfuric dye I（SD1）） are tested experimentally under the same illumination intensity （450 nm, 80 mW/cm2）. The results demonstrate that with a suitable liquid crystal, the LC optical rewriting speed for e-paper application can be obviously improved. For two well known LC materials E7 （K22 is larger） and 5CB （K22 is smaller）, they require 11 s and 6 s corresponding to change alignment direction for generating image information.     

Electronic and Optical Properties of Rock-Salt AIN under High Pressure via First-Principles Analysis

Electronic and optical properties of rock-salt AIN under high pressure are investigated by first -principles method based on the plane-wave basis set. Analysis of band structures suggests that the rock-salt AIN has an indirect gap of 4.53 eV, which is in good agreement with other results. By investigating the effects of pressure on the energy gap, the different movement of conduction band at X point below and above 22.5 GPa is predicted. The optical properties including dielectric function, absorption, reflectivity, and refractive index are also calculated and analyzed. It is found that the rock-salt AIN is transparent from the partially ultra-violet to the visible light area and hardly does the transparence affected by the pressure. Furthermore, the curve of optical spectrum will shift to high energy area （blue shift） with increasing pressure.     

Effect of substrate temperature on microstructure and optical properties of single-phased Ag20 film deposited by using radio-frequency reactive magnetron sputtering method

Using a radio-frequency reactive magnetron sputtering technique, a series of the single-phased Ag20 films are deposited in a mixture of oxygen and argon gas with a flow ratio of 2：3 by changing substrate temperature （Ts）. Effects of the Ts on the microstructure and optical properties of the films are investigated by using X-ray diffractometry, scanning electron microscopy and spectrophotometry. The single-phased Ag20 films deposited at values of Ts below 200℃ are （111） preferentially oriented, which may be due to the smallest free energy of the （111） crystalline face. The film crystallization becomes poor as the value of Ts increases from 100℃ to 225℃. In particular, the Ag20 film deposited at Ts=225℃ loses the （111） preferential orientation. Correspondingly, the film surface morphology obviously evolves from a uniform and compact surface structure to a loose and gullied surface structure. With the increase of Ts value, the transmissivity and the reflectivity of the films in the transparent region are gradually reduced, while the absorptivity gradually increases, which may be attributed to an evolution of the crystalline structure and the surface morphology of the films.     

On-chip optical pulse shaper for arbitrary waveform generation

We propose and demonstrate a silicon-on-insulator(SOI) on-chip optical pulse shaper based on four-tap finite impulse response. Due to different width designs in phase region of each tap, the phase differences for all taps are controlled by an external thermal source, resulting in an optical pulse shaper. We further demonstrate optical arbitrary waveform generation based on the optical pulse shaper assisted by an optical frequency comb injection. Four different optical waveforms are generated when setting the central wavelengths at 1533.78 nm and 1547.1 nm and setting the thermal source temperatures at 23℃ and 33℃, respectively. Our scheme has distinct advantages of compactness, capability for integrating with electronics since the integrated silicon waveguide is employed.     

Effects of shape and dopant on structural,optical absorption,Raman, and vibrational properties of silver and copper quantum clusters: A density functional theory study

We investigate the effects of shape and single-atom doping on the structural, optical absorption, Raman, and vibra- tional properties of Ag13, Ag12CUl, CUl3, and Cul2Agl clusters by using the （time-dependent） density functional the- ory. The results show that the most stable structures are cuboctahedron （COh） for Ag13 and icosahedron （Ih） for CUl3, Agl2CUlcore, and Cul2Aglsur. In the visible-near infrared optical absorption, the transitions consist of the interband and the intraband transitions. Moreover, red shifts are observed as follows： 1） clusters change from Agl2CUlcore to Ag13 to Ag12Culsur with the same motifs, 2） the shapes of pure Agl3 and Agl2CUlcore clusters change from COh to Ih to decahe- dron （Dh）, 3） the shape of Agl2CUlsur clusters changes from Ih to COh to Dh, and 4） the shapes of pure CU13 and Cu12Agl clusters change from Ih to Dh to COb. All of the Raman and vibrational spectra exhibit many significant vibrational modes related to the shapes and the compositions of the clusters. The ranges of vibrational spectra of Ag13, Agl2CUl or CU13, and Cu12Agl clusters become narrower and the vibrational intensities increase as the shape of the clusters changes from Ih to Dh to COh.     

η-nucleus bound states in nuclei

The binding energies εη and widths Гη of wmesic nuclei are calculated. We parameterize the η self-energy in the nuclear medium as a function of energy and density. We find that the single-particle energies are sensitive to the scattering length, and increase monotonically with the nucleus. The key point for the study of η-nucleus bound states is the η-nuclear optical potential. We study the s-wave interactions of η mesons in a nuclear medium and obtain the optical potential Uη ≈ -72 MeV. Comparing our results with the previous results, we find that the ηN scattering length aηN is indeed important to the calculations. With increasing nuclear density the effective mass of the η meson decreases.