The determination of the x value in doped Hg_(1-x)Cd_x Te by transmission spectra

Variable-temperature transmission/absorption spectra are measured on As-doped Hgl-xCdxTe grown by molec- ular beam epitaxy. The nonlinear temperature-dependent shift of the absorption edge is also observed, which is similar to our previous report on VHg （unintentionally）-doped HgCdTe. By referring to the empirical formulas of Eg（x,T）, the x value of the epilayer is calculated and its inconsistency between the extreme temperatures （e.g. 10 and 300 K） is discussed. The results confirm the assumption of the effect of shallow levels on the shift of the absorption edge, and suggest that the x value （or Eg） in intrinsic/extrinsic-doped HgCdTe should be determined by referring to as low a temperature as possible （e.g. 10 K）, and not the commonly used temperatures of 77 or 300 K, when the transmission spectrum should be employed. This can give brief guidelines for fabricating HgCdTe-related devices.

Bandpass transmission spectra of a whisperinggallery microcavity coupled to an ultrathin fiber

Tapered fibers with diameters ranging from 1 to 4 μm are widely used to excite the whispering-gallery(WG)modes of microcavities. Typically, the transmission spectrum of a WG cavity coupled to a waveguide around a resonance assumes a Lorentzian dip morphology due to resonant absorption of the light within the cavity. In this paper, we demonstrate that the transmission spectra of a WG cavity coupled with an ultrathin fiber(500–700 nm)may exhibit both Lorentzian dips and peaks, depending on the gap between the fiber and the microcavity. By considering the large scattering loss of off-resonant light from the fiber within the coupling region, this phenomenon can be attributed to partially resonant light bypassing the lossy scattering region via WG modes, allowing it to be coupled both to and from the cavity, then manifesting as Lorentzian peaks within the transmission spectra.This implies the system could be implemented within a bandpass filter framework.

Ultrafast Carrier Dynamics in CdSe/CdS/ZnS Quantum Dots

The intra- and inter-band relaxation dynamics of CdSe/CdS/ZnS core/shell/shell quantum dots are investigated with the aid of time-resolved nonlinear transmission spectra which are obtained using femtosecond pump-probe technique. By selectively exciting the core and shell carrier, the dynamics are studied in detail. Carrier relaxation is found faster in the conduction band of the CdS shell （about 130 fs） than that in the conduction band of the CdSe core （about 400 fs）. From the experiments it is distinctly demonstrated the existence of the defect states in the interface between the CdSe core and the CdS shell, indicating that ultrafast spectroscopy might be a suitable tool in studying interface and surface morphology properties in nanosystems.

Influence of dopant content on morphology and optical constants of ZnO:Na films by sol-gel method

Undoped and Na-doped ZnO films were deposited by sol-gel method.The effects of sodium incorporation on structure,surface morphology and optical constants of the films were investigated.X-ray diffraction patterns show the hexagonal wurtzite polycrystalline structure and that the sodium incorporation leads to the change in the structural characteristics of ZnO films.The SEM observations show that the surface morphology of the films is affected by the sodium incorporation.The transmission spectra show that the average transmittance of the films is above 85% in the visible range.The absorption edge initially blue-shifts and then red-shifts with the increase of Na doping content.The optical constants of these films were calculated using transmission spectra.Refractive indices of the films in the visible range decrease at first and then increase with increasing Na doping content.

Growth and Characterization of High-quality LiAlO2 Single Crystal

γ-LiAlO2 single crystal is a promising substrate for GaN heteroepitaxy. In this paper, we present the growth of large-sized LiAlO2 crystal by modified Czochralski method. The crystal quality was characterized by high-resolution X-ray diffraction and chemical etching. The results show that the as-grown crystal has perfect quality with the full width at half maximum （FWHM） of 17.7-22.6 arcsec and etch pits density of （0.3- 2.2）×10^4 cm^-2 throughout the crystal boule. The bottom of the crystal boule shows the best quality. The optical transmission spectra from UV to IR exhibits that the crystal is transparent from 0.2 to 5.5μm and becomes completely absorbing around 6.7μm wavelength, The optical absorption edge in near UV region is about 191 nm.

Coupled resonator-induced transparency on a three-ring resonator

The coupled resonator-induced transparency （CRIT） phenomenon, which is analogous to electromagnetically induced transparency in atomic systems, can occur in an original integrated optical resonator system due to the coherent interference of the coupled optical resonators. The system was composed of three ring resonators on silicon, each with the same cavity size, and the optical coupling to the input and output ports was achieved using grating with a power coupling efficiency of 36%. A CRIT resonance whose spectrum shows a narrow transparency peak with a low group velocity was demonstrated. The quality factor of the ring resonator can attain a value up to 6x 104, and the harmonic wavelength can be controlled by adjusting the temperature. The through and drop transmission spectra of the resonator are reconciled well with each other and also consistent well with the theoretical analysis.

Magneto-Optic Fiber Bragg Gratings with Application to High-Resolution Magnetic Field Sensors

Magneto-optic fiber Bragg gratings （MFBG） based on magneto-optic materials have a lot of potential applications for sensing and optical signal processing. The transmission and reflection spectra of guided optical waves in the MFBG are investigated. According to the sensitivity of MFBG spectral lines to the magneto-optic coupling intensity varying with applied magnetic field, a novel magnetic field sensor of high-resolution up to 0.01 nm/（kA/m） is predicted.

Plasmon resonance coupling in strongly coupled gold nanotube arrays with structural defects

We theoretically investigate the transmission spectra and the field distributions with different defects in the gold nanotube arrays by using the finite-difference time-domain method. It is found that the optical properties of the nanotube arrays are strongly influenced by different defects. When there are no defects in the central nanotube, the values of peaks located at both sides of the photonic band gap have their maxima. Based on the distributions of electric field component Ex and the total energy distribution of the electric and the magnetic field, we show that mainly a dipole field distribution is exhibited for the plasmon mode at the long-wavelength edge of the band gap but higher order modes of the composite are excited at the short-wavelength edge of the band gap. The plasmon resonant modes can also be controlled by introducing defects.

Electron tunneling through double-electric barriers on HgTe/CdTe heterostructure interface

We investigate theoretically the carrier transport in a two-dimensional topological insulator of(001)HgTe/CdTe quantum-well heterostructure with inverted band,and find distinct switchable features of the transmission spectra in the topological edge states by designing the double-electric modulation potentials.The transmission spectra exhibit the significant Fabry–Pérot resonances for the double-electric transport system.Furthermore,the transmission properties show rich behaviors when the Fermi energy lies in the different locations in the energy spectrum and the double-electric barrier regions.The opacity and transparency of the double-modulated barrier regions can be controlled by tuning the modulated potentials,Fermi energy and the length of modulated regions.This electrical switching behavior can be realized by tuning the voltages applied on the metal gates.The Fabry–Pérot resonances leads to oscillations in the transmission which can be observed in experimentally.This electric modulated-mechanism provides us a realistic way to switch the transmission in edge states which can be constructed in low-power information processing devices.

Electronic Transport Properties of Transition-Metal Terminated Trigonal Graphene Nanoribbons

With the non-equilibrium Green’s function method and density functional theory, we have studied the electronic properties of trigonal graphene nanoribbons, with Fe terminal and H terminal, coupled to gold electrodes. Rectification behavior can be observed when the electrode-molecule contact distance is larger than 2.2 &Aring. The electronic transport is greatly improved in case of Fe terminal which is analyzed in terms of transmission spectra and density of states.

Boundary element method for calculation of elastic wave transmission in two-dimensional phononic crystals

A boundary element method(BEM) is presented to compute the transmission spectra of two-dimensional(2-D) phononic crystals of a square lattice which are finite along the x-direction and infinite along the y-direction.The cross sections of the scatterers may be circular or square.For a periodic cell,the boundary integral equations of the matrix and the scatterers are formulated.Substituting the periodic boundary conditions and the interface continuity conditions,a linear equation set is formed,from which the elastic wave transmission can be obtained.From the transmission spectra,the band gaps can be identified,which are compared with the band structures of the corresponding infinite systems.It is shown that generally the transmission spectra completely correspond to the band structures.In addition,the accuracy and the efficiency of the boundary element method are analyzed and discussed.

Spatial-dependent probe transmission based high-precision two-dimensional atomic localization

Herein,we propose a scheme for the realization of two-dimensional atomic localization in aλ-type three-level atomic medium such that the atom interacts with the two orthogonal standing-wave fields and a probe field.Because of the spatially dependent atom-field interaction,the information about the position of the atom can be obtained by monitoring the probe transmission spectra of the weak probe field for the first time.A single and double sharp localized peaks are observed in the one-wavelength domain.We have theoretically archived high-resolution and high-precision atomic localization within a region smaller thanλ/25×λ/25.The results may have potential applications in the field of nano-lithography and advance laser cooling technology.

Influence of In^(3+) ions concentration on spectroscopic properties of Ho:LiNbO_3 crystals

In：Ho：LiNbO3 crystals doped with various concentrations of In3＋（0, 1 mol.%, 3 mol.%, 5 mol.%）, fixed concentrations of Ho3＋ （1 mol.%） were grown by Czochralski method. The X-ray powder diffraction, infrared and UV-visible absorption spectra were measured and modified. Judd-Ofelt approach was employed to study the effect of In doping on spectroscopic properties of Ho：LiNbO~ crystals. In con- centrations in crystals were analyzed by an inductively coupled plasma optical emission spectrometry （ICP-OE/MS）. For In （3 mol.%）：Ho （1 mol.%）：LiNbO3 crystal, the obtained intensity parameters were： Ω2=9.6563, Ω4-4.2195, Ω6-14.1526. The results showed that the Ω2 and Ω6 parameters increased with the increase of In3＋ concentration. When the In doping concentration was up to 5 tool.%, Ω2 and Ω6 suddenly decreased. In2O3 incorporation had a strong effect on the radiative lifetime, but had less influence on fluorescence branching ra- tios. The effective distribution coefficient of In3＋ in In：Ho：LiNbO3 crystals was less than 1 and increased with increasing concentration of In3＋ in the melt.