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A general method is proposed to describe the energy levels of the interface states in one-dimensional photonic crystal (PC) heterojunction [Formula: see text] containing dispersive or non-dispersion materials. We found that the finite energy levels of the interface states for the finite configuration can be described totally by the dispersion relation of the PC with a periodic unit [Formula: see text]. It is further found that this method is also applicable for the case of defect modes. We believe our method can be used to guide the practical application.

The zero-refraction property of a metal film can be used to image so that the metal film behaves as a superlens. Experimentally, the metal superlens is sandwiched between the photosensitivity resist (PR) and the dielectric spacer in the photolithograph device to produce images. In this paper, the imaging conditions of the metal superlens, or the parameters of the device containing the superlens are investigated in detail. It is found that the energy zero-refraction effect is the intrinsic property of the metal superlens. The permittivities of the dielectrics at the two sides of the superlens will influence the imaging quality. The rule is drawn for obtaining best images: the two dielectrics should have the same permittivities, so-called symmetry case, and the real part of the permittivity of the metal superlens plus the dielectric permittivity is just equal to 1, i.e. ϵ ( dielectric ) + ϵ r ( superlens ) = 1 .

In this paper, Dirac point method is used to study the interface state of one-dimensional photonic crystal heterojunction [Formula: see text] containing dispersive materials GaAs. We found that the energy levels of the interface states satisfy a simple sinusoidal function. We investigate the variation of the energy levels of the interface states with the incident angle, it is found that these interface states move toward high-frequency with the increase of the incident angle. At the same time, it is found that there is an extra localized band and it is further proved that the extra band corresponds to the defect band, and the energy levels of the defect band possess the same behavior with those of interface states.

A tunable optical unidirectional device or optical isolator composed of a metal subwavelength grating covered with magneto-optical rotation medium is proposed. The results of a simulation show that the difference of transmissivity in opposite directions varies from 0 to 83% with an external magnetic field at room temperature. The largest field needed to control transmissivity is only 1.1 T, so the working conditions can be easily achieved. A theoretical method to calculate transmissivity is presented and the unique transmission characteristics of this new device are explained satisfactorily.

The mechanism of the unidirectional transmission in metal subwavelength gratings with different surfaces is investigated theoretically. This kind of unidirectional transmission belongs to the extraordinary optical transmission assisted by the surface plasmon polariton (SPP). The SPP wave comes through the multi-reflection process and finally transforms into the transmission wave. The difference of amplitude transmissivities and reflectivities at different surfaces in opposite incident directions results in the unidirectional transmission. A division method is proposed to calculate the parameters of subwavelength gratings with asymmetric surfaces.

This paper studies optical transmission through an interface between two slits with different widths in a sheet composed of an ideal conductor. Such a structure is of potential use in fabricating optical diode and may be the simplest one compared to other designs. Our calculations show that there is a critical wavelength. When the light wavelength is below the critical wavelength, the transmissivity is unidirectional. The expression of the stable transmissivity as a function of the ratio of the widths of the two slits was obtained analytically. Particularly, at the critical wavelength, the transmissivities are zero. This phenomenon has great potential for application in the manufacture of wavelength blockers.

The nanostructure of amorphous carbon thin film is described in terms of a disordered conductive sp2 phase embedded in an electrically insulating sp3 matrix. The conductive sp2 phase is dominated by Drude type free-carries response, and the carrier conductive between sp2 clusters is hopping. The two conductivities are in a serial configuration under a percolation approximation. In view of this, we extend Shimakawa’s model for compact nanoparticles [14] to amorphous carbon thin films in order to provide understanding on its terahertz (THz) optical complex permittivity. Furthermore, the contribution of phonons for THz optical complex permittivity is included in the scope of Debye theorem phenomenologically. Considering the condition of ω ω TO and the narrow frequency range, we interpret the complex phonon permittivity experimentally as e phonon = A ω e i θ for amorphous carbon. Thus, the real and imaginary permittivity can be simultaneously explained by the above considerations. It is the first qualified analysis on the THz optical properties of amorphous carbon thin films experimentally.

In this paper, the magnetic properties of ferromagnetic graphene nanostructures, especially the dependence of the magnetism on finite temperature, are investigated by use of the many-body Green’s function method of quantum statistical theory. The spontaneous magnetization increases with spin quantum number, and decreases with temperature. Curie temperature increases with exchange parameter J or the strength K2 of single-ion anisotropy and spin quantum number. The Curie temperature TC is directly proportional to the exchange parameter J. The spin-wave energy drops with temperature rising, and becomes zero as temperature reaches Curie temperature. As J(p,q)=0, ω1=ω2, the spin wave energy is degenerate, and the corresponding vector k=(p, q) is called the Dirac point. This study contributes to theoretical analysis for pristine two-dimensional magnetic nanomaterials that may occur in advanced experiments.

In this paper, the effect of Nb doping on the formation of O vacancies in rutile TiO2 is studied by the use of ab initio density-functional calculations. The formation energies are calculated at different doping concentrations (CNb) and the corresponding electronic structures are analyzed. It is shown that the formation energy is mainly determined by the structural relaxation. As CNb increases, the formation energy first increases and then decreases with the maximum in vicinity of CNb=11.1 at%. The investigation of electronic structures shows that the distribution of excess electrons, which is affected by the doping concentration and the types of oxygen vacancy, determines the relaxation and formation energy of oxygen vacancy. Our calculated results indicate that the formation of oxygen vacancy in rutile TiO2 can be most effectively suppressed by Nb doping in a large range of Nb doping concentration. This may be one of the reasons why the proper amount of Nb doping can improve the oxidation resistance of γ - TiAl .

The magnetic behaviors of ferromagnetic single-walled nanotubes are systematically investigated by use of the many-body Green's function method of quantum statistical theory. The spontaneous magnetization, absolute value of ferromagnetic energy, area of hysteresis loop and coercivity increase with diameter of the tubes and spin quantum number, and decrease with temperature. Curie temperature increases with diameter and spin quantum number. As the diameter of the tube tends to infinity, all the numerical results approach to those of a two-dimensional monolayer. The dependences of initial susceptibility on temperature and diameter below and above Curie point are contrary. The calculated results are compared with experimental results where possible, and are qualitatively in agreement with the latter. The Curie temperature is determined by the tube diameter and independent of rolling helicities.

We report an intense (∼10mW) and ultra-broadband (∼150 THz) THz to infrared (IR) source with a Gaussian wavefront, emitted from nano-pore-structured metallic thin films with femtosecond laser pulse excitation. The underlying mechanism has been proposed as thermal radiation. In addition, an intense coherent THz signal was generated through the optical rectification process simultaneously with the strong thermal signal. This unique feature opens up new avenues in biomedical research.

One kind of optical unidirectional transmission structures is proposed which is composed of a metal subwavelength slit dressed by one or two gratings. Simulation results show that the gratings with different geometry parameters can play different roles. One role is the convergence effect and the other is shield effect. Each effect can independently cause the unidirectional transmission with special properties. These two effects are explained in view of optical reciprocal theorem. Combination of the two effects results in excellent unidirectional transmission properties.

Terahertz (THz) spectroscopic sensing and imaging has identified its potentials in a number of areas such as standoff security screening at portals, explosive detection at battle fields, bio-medical research and so on. With these needs, the development of an intense and broadband THz source has been a focus of THz research. In this work, we report an intense (~10 mW) and ultra-broadband (~150 THz) THz to infrared (IR) source with a Gaussian wavefront, emitted from nano-pore-structured metallic thin films with femtosecond laser pulse excitation. The underlying mechanism has been proposed as thermal radiation. In addition, an intense coherent THz signal was generated through the optical rectification process simultaneously with the strong thermal signal. This unique feature opens up new avenues in biomedical research.

We calculate the omnidirectional dispersion spectrum for one-dimensional (1D) photonic crystals (PCs) inserting multiple photonic quantum-wells (PQWs) with the use of the plane-wave expansion method in combination with a supercell technique. We find that the localized defect modes significantly depend on the number of the PQWs and the configuration. This may provide a new way to engineer the dispersions of the composite PCs to meet the requirements of optical or microwave devices.

The parametric amplification (PA) and second harmonic generation (SHG) from quasi-one-dimensional aperiodic optical superlattices (AOSs) are investigated in the cases of large, intermediate, and small signals of the pumping light wave. The optimal design of the AOSs is carried out with the use of the simulated annealing (SA) method. The numerical simulations show that the constructed AOSs can achieve multiple wavelength PA (or SHG) with identical amplification (or identical conversion efficiency) at the pre-assigned wavelengths. The variations of the normalized intensities of the PA signal (or the pumping fundamental wave (PFW)) for the PA process with the distance of propagation of the light wave from the interface of the AOSs at the pre-assigned wavelengths exhibit monotonically increasing (or decreasing) behavior. So do the variations of the normalized intensities of the second harmonic wave (SHW) (or the fundamental wave (FW)) for the SHG. This strongly supports the fact that the contribution of each individual unit domain in the constructed samples to the PA (or SHG) is constructive accumulation, favorable for the PA (or SHG) process. The saturation phenomenon of the PA (or SHG) signal is observed.

We investigate the evolution of the band gap in one-dimensional (1D) photonic crystals (PC) with the gradual modifications of structural configurations from photonic quantum wells to PC heterostructures. The transmissive spectra are calculated with the use of scattering matrix method. We find that the transmissive spectra and confined states strongly depend on the structural configurations of samples.

The structural and magnetic properties of Co–Pt/C nanocomposite films were investigated as functions of Pt and C concentration, respectively. Under the same conditions two series multilayer samples with different Pt and C concentrations were prepared. The as-deposited films are amorphous Co–Pt–C alloys and magnetically soft. All samples were annealed in vacuum. The lattice structure is observed to transform and grain size is reduced to 7 nm. These structural transitions are accompanied by large changes in magnetic anisotropy. A maximum coercivity of approximately 5.4 kOe is obtained and a shoulder in hysteresis loops develops. These results show that Co–Pt particles are transformed by annealing from a disordered phase to ordered face-centered-cubic CoPt3 and face-centered-tetragonal CoPt, commixed in a C matrix, and the various Co–Pt crystalline particles interact.

Co–Pt/C alloy films with parallel magnetic anisotropy, 90% remanence, and large coercivity were prepared by sputtering on Si substrate in multilayer form and post-annealing in vacuum at 700 °C for 1 h. Effects of Pt and Co concentration on the magnetic properties of the films are studied. The shoulder developed on the hysteresis loop is analyzed.

We investigate the properties of guide modes localized at the interfaces of photonic crystal (PC) heterostructures which are composed of two semi-infinite two-dimensional PCs consisting of non-circular air cylinders with different rotating angles embedded in a homogeneous host dielectric. Photonic band gap structures are calculated with the use of the plane-wave expansion method in combination with a supercell technique. We consider various configurations, for instance, rectangular (square) lattice–rectangular (square) air cylinders, and different rotating angles of the cylinders in the lattices on either side of the interface of a heterostructure. We find that the absolute gap width and the number of guide modes strongly depend on geometric and physical parameters of the heterostructures. It is anticipated that the guide modes in such heterostructures can be engineered by adjusting parameters.

We first investigate the band gap structures of two-dimensional magnetic photonic crystals (MPC) composed of rectangular (square) magnetic cylinders embedded in a host dielectric material in the rectangular (square) lattice, and we then study guide modes at interface of MPC heterostructures (MPCHs) by use of plane wave expansion method in combination with supercell technique. We find that both the mirror-symmetric MPCHs and the mixed-type MPCHs composed of square cylinders in a square lattice can produce the TM guide modes even without any lattice distortions. This feature is quite different from that of the non-magnetic PC heterostructures, in which the occurrence of the guide modes requires the relatively longitudinal gliding or transverse displacement of lattices. It may provide a new way to generate guide modes and apply to the device of light wave guides.

Monolayer (ML) hexagonal (2H) WTe2 is predicted to be the best channel material of tunnel field effect transistor (TFET) and metal–oxide–semiconductor field effect transistor (MOSFET) among ML transition-metal dichalcogenides. Actual devices based on 2H WTe2 typically have a contact with metal. We explore for the first time the interfacial properties between ML 2H WTe2 and Sc, Ti, Pd, Pt, Ag, and Au by using ab initio electronic structure calculation and ab initio quantum transport simulations. The energy bands of ML 2H WTe2 on Sc, Ti, Pd, and Pt substrates are destroyed strongly due to strong adhesion of ML 2H WTe2 with metal substrates, and ML 2H WTe2–Sc, −Ti, −Pd, and −Pt systems are regarded as new metallic materials. Weak adhesion is formed between ML 2H WTe2 and the Ag and Au surfaces, with the electronic energy band of ML 2H WTe2 being identifiable. Ag and Au form n-type Schottky contact with ML 2H WTe2 at the vertical direction with electron Schottky barrier height (SBH) of 0.24 and 0.49 eV, respectively. In contrast, Pd, Pt, and Ti form p-type Schottky contact with ML 2H WTe2 in the lateral direction with hole SBH of 0.26, 0.40, and 0.63 eV, respectively. Our study not only presents a theoretical insight into the ML 2H WTe2–metal interfaces but also help in ML 2H WTe2 based device design.

By the multiple reflections and transmissions in a dielectric on a ferromagnetic metal, color and Kerr rotation correlate with each other. It is revealed that the real refractive index of dielectric plays a major role on the variations of color and Kerr signal, while the absorbing term adjusts the intensive color exhibition and Kerr enhancement at much thinner dielectric thickness. The intensive Kerr signal variation is always accompanied by the color transition with the dielectric thickness changing. Experimental results observed in silicon(or silica)/iron samples are well consistent with calculations. Nanometer dielectric optical coating can not only enhance Kerr effect but also endow magnetic surface with chromatics, which has promising potential applications in anti-fake brands, colorful decorations, camouflages, and even bionics.

Based on measured data of HSS (high-speed steel) and HCr (highchromium iron) work rolls applied in 1580mm HSM (hot strip mills) with mass production of electrical steel strip, an HSS work roll wear prediction model in upstream stands for non-oriented electrical steel strip rolling was established by genetic algorithm. The accuracy of the model was verified and could guide practical production.

The integration effects on flatness control during hot rolling process is studied for meeting the requirement of schedule-free rolling (SFR) campaigns of non-oriented electrical steel strips with identical width. A 3D finite element model for elastic deformation of rolls is built by ANSYS. The integration effects of lubrication, asymmetry self-compensating work rolls (ASR), and varying contact back-up roll (VCR) contours on flatness control are comparatively analyzed. An improved strip profile, flatness, and rolling stability are achieved by combining these technologies. The total rolling coil number is increased from 70 to 100 within a rolling campaign. The lateral stiffness of roll gap is increased by 10.3 and 12.75% in the early and later rolling stage, respectively.

The one-way devices in optical circuits are the key components just as the diodes in electric circuits, which allow the light going in only one direction. A novel one-way transmission structure is proposed which is a curved waveguide containing a confined photonic crystal. When the waveguide is made of perfect electric conductor, the exact calculation results demonstrate that the device shows excellent one-way properties. The forward transmissivity approaches 100% and the largest transmission ratio exceeds 100.92N, where N is the cell number of the photonic crystal in the structure. When the waveguide is made of real metal, the device also presents excellent one-way transmission properties, which can be confirmed by an approximate calculation as well as by the simulation. In working region, the lowest forward tranmissivity is about 30% and the largest one exceeds 70%. The highest transmission ratio exceeds 104.

The change of the electronic structure of La 1.85 Sr 0.15 CuO 4 caused by the local substitution of Zn for Cu has been calculated by the recursion method. The partial wave density of states, the intensity of bonds, and the atomic valence, etc. are obviously affected by Zn on the doped site and its neighbors. The 2D electronic structure and magnetic structure are destroyed locally. We think these, together with the local increase of Cu holes, decrease of O2 holes, and the inducement of a net magnetic moment of 1.3 µB are responsible for the rapid suppression of superconductivity in Zn-doped La 1.85 Sr 0.15 CuO 4 materials.

We found that a single negative material has a character of zero-refraction in near field, and point out that the mechanism of a metal superlens to image with the resolution exceeding the diffraction limitation is different from that of a perfect lens made of a double negative material. The principle of metal superlens is disclosed. Our numerical results based on the zero-refraction character coincide with the experimental results well. This work brings new understanding about the single negative materials and will lead the applications of metal superlens in right way., 11 pages, 4 figures

We investigate the mechanism of extraordinary optical transmission in subwave-length metal hole arrays. Experimental results for the arrays consisting of square or rectangle holes are well explained about the dependence of transmission strength on the polarization direction of the incident light. This polarization dependence occurs in each single-hole. For a hole array, there is in addition an interplay between the adjacent holes which is caused by the transverse magnetic field of surface plasmon polariton on the metal film surfaces. Based on the detailed study of a single-hole and two-hole structures, a simple method to calculate the total tranmissivity of hole arrays is proposed., Comment: 34 pages, 7 figures

We investigate the extraordinary optical transmission of a subwavelength elliptic hole array in a metal by a proposed simple method. The transmission strength depends on the polarization direction of the incident light. The polarization excitation ratio of the surface plasmon polariton (SPP) governs the transmissivity. There is an interplay between the adjacent holes which is caused by the transverse magnetic filed of SPP on the surfaces of the metal.

The critical temperature Tc of a spin-1/2 Ising film of cubic structures is calculated by the variational cumulant expansion method for three directions of growth. The results from different growth directions are analysed and compared with each other. In the present model, the Tc values depend largely on the number of nearest neighbors in a monolayer for films with the same number of monolayers but grown in different directions. For sc, bcc and fcc structures, the highest Tc is found along the (100), (110), and (111) direction, respectively.

We present the time-domain analysis of the extraordinary optical transmission of the slits milled on the thin metallic film. We employ the finite-difference time-domain method to study the variations of the transmission energies with the sampling time received by several monitors that are placed on the specified positions in the structure. It is found that the physical origin of the related phenomenon may be contributed by a combining effect of single-slit effect and interslits effect. The single-slit effect is brought by the excitation of surface-plasmon polaritons from the isolated slit and the interslits effect is caused by phase interference of the transmitted waves from two slits. When the transmissivity of an isolated slit is adjusted to a maximum, total transmissivity of the grating is never governed by phase interference and can be qualified to the contribution from a single slit alone.

A new method, namely the nonlinear conjugate-gradient (NCG) method, is proposed to design nonlinear domains with a disordered distribution, in which an efficient broadband second harmonic generation can be achieved simultaneously with high conversion efficiency. It is demonstrated by numerical simulation that the NCG method has obvious advantages in realizing the optimal quasi-phase-matching, in comparison with the traditional simulated annealing method.

We demonstrate theoretically that an optical one-way transmission device can be constructed by inserting an epsilon-near-zero (ENZ) prism into a metal slit. Similarly to the junction in the electron diode, the oblique surface of the ENZ prism is a key factor that can block the transmission of the light striking on it and allows the transmission of the light leaving from it. The performance of the device is shown by numerical simulation based on the finite-difference time-domain technique.

We calculate the lifetime distribution function of an assembly of polarized atoms in two-dimensional (2D) photonic crystals (PCs) at different polarization orientations of atomic dipole moments. We reveal a switching effect of atomic spontaneous emission (SE) and find a significant change of atomic lifetime, up to a factor of 33, by tuning the polarized orientation of the atoms. These observations suggest that the tuning of the polarized orientation of atoms provides a new way for the effective control of atomic SE processes in 2D PCs.

The lifetime distribution functions of the spontaneous emission (SE) of the excited atoms embedded in two-dimensional (2D) photonic crystals (PCs) with square lattice, consisting of square air rods in dielectric medium with different filling factors, are calculated by using the plane wave expansion method. The numerical results show that the SE in the 2D PCs cannot be prohibited completely but it can be inhibited intensively by the pseudo-PBG of the PCs. In the pseudoband edges, the SE is accelerated obviously. The reduced average lifetime of the excited atoms and the extension of the reduced lifetime distribution in the 2D PCs both are the same as those in the 3D PCs in the order of magnitude. Our results provide an available way to control the behavior of the SE by changing the structures of the 2D PCs.

In this presentation, we investigate the properties of the PBG's in the MPC's in detail. We calculate the band structures of two-dimensional (2D) MPC's which are composed of magnetic rectangular/square scatterers in rectangular/square lattice. The plane-wave expansion method is employed. We find that the PBG's in the MPC's strongly depend on physical and geometric parameters in the structures, such as the shapes of the 2D lattice and the scatterers, the permeability of the scatterers, and so on. Therefore, the introduction of magnetic material into the PC's may diversify the favorable candidates of the PC's in nature. It is expected that the PBG's in the MPC's can be engineered by changing the relevant parameters to match various practical applications in optical devices.

The so-called quasi-phase-matching (QPM) for second-harmonic generation (SHG) considering depletion of the pumping light power is amended. The conversion efficiency of SHG and the optimum domain width are discussed. The applicable scope of undepleted pump approximation (UPA) is estimated and a relative tolerance showing the difference in the SHG between the UPA and the pump depletion is solely determined by the SHG conversion efficiency. A model is fitted using the relevant data, and the results reveal that the conversion efficiency of SHG can be conveniently and easily assessed under the given conditions of pump intensity, the nonlinear media and the number of domains. The optimum domain widths deviate from the coherence length lc = π/Δk. The deviation increases with the pump intensity, but there is little impact on SHG due to system variations in crystal length.

In this paper, we applied the band structure theory to investigate the plasmonic band (PB) structures and optical properties of subwavelength metal/dielectric/metal Bragg waveguides in the near infrared range with either dielectric or geometric modulation. The Bloch wave vector, density of states, slowdown factor, propagation length and transmittance are calculated and analyzed. Both the modulations are in favor of manipulating surface-plasmon-polariton (SPP) waves. For the dielectric modulation, the PB structure is mainly formed by SPP modes and possesses a "regular pattern" in which the bands and gaps have a relatively even distribution. For the geometric modulation, due to the strong transverse scattering, the contributions of higher modes have to be considered and the gap widths have a significant increase compared to the dielectric modulation. A larger slowdown factor may emerge at the band edge; especially for the geometric modulation, the group velocity can be reduced to 1/100 of light, and negative group velocity is observed as well. While inside the bands, the slowdown factor is smaller and the bands are flat. The contribution of each eigenmode to the PB structure is analyzed.

We develop a theoretical formalism that incorporates the method of moment with the analytical eigenmode expansion to investigate the dispersion relation of light transport in subwavelength metallic Bragg waveguide (WG) with each unit cell composed of a wide and a narrow segment of metallic gap. The approach fully accounts for the light scattering at the interface between two consecutive discontinuous segments. A simple single-mode analytical model is derived for both the fundamental even and odd guided modes. The model shows that the band structure of light transport in the structure resembles that of an ordinary dielectric one-dimensional photonic crystal with appropriate physical and geometric parameters that can be analytically derived. Numerical simulations by the finite-difference time-domain method on the optical transmission spectra and band diagrams for these metallic Bragg WGs agree well with the analytical results of band diagrams. In addition, the analytical model can handle structures working in both the microwave and infrared regimes. This indicates that the simple analytical model is effective and efficient in handling various light transport problems for subwavelength metallic Bragg WGs.

The process of the light passing through a single subwavelength metal slit is analyzed by the finite-difference time-domain method. The simulation results show that the slit can be considered as an effective dielectric region sandwiched by two scattering regions at the two slit ends. Thus, the slit is analogous to a Fabry-Perot (FP) etalon consisting of a dielectric slab with high-reflection coatings on its two surfaces. A formula is presented to evaluate the phase shift caused by the amplitude transmissivity of the coatings.

We investigate one-dimensional nonlinear photonic crystals consisting of ferroelectric domains with the modulated polarization direction. The optimal arrangement of the polarization directions of the ferroelectric domains can be achieved with the use of the simulated annealing method. We find that the second-harmonic generation (SHG) is increased significantly when the frequencies of the fundamental wave aim at the photonic band edges and the special arrangement of the polarization directions of the ferroelectric domains is satisfied. The optimal structure can achieve simultaneously multiple wavelength SHGs with nearly identical conversion efficiencies for both the “forward” and “backward” SHGs.

We use the transfer-matrix method to research the band structures in one-dimensional photonic crystals composed of anomalous dispersion material (saturated atomic cesium vapor). Our calculations show that that type of photonic crystal possesses an ultra-narrow photonic band gap and this band gap is tunable when altering the electron population in the atomic ground state of the anomalous dispersion material by the optical pumping method.