Orientation effects on the bandgap and dispersion behavior of 0.91Pb(Zn_1/3Nb_2/3)O₃-0.09PbTiO₃ single crystals

0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO 3(PZN-9%PT) single crystals with different orientations are investigated by using a spectroscopic ellipsometer,and the refractive indices and the extinction coefficients are obtained.The Sellmeier dispersion equations for the refractive indices are obtained by the least square fitting,which can be used to calculate the refractive indices in a low absorption wavelength range.Average Sellmeier oscillator parameters E o,λ o,S o,and E d are calculated by fitting with the single-term oscillator equation,which are related directly to the electronic energy band structure.The optical energy bandgaps are obtained from the absorption coefficient spectra.Our results show that the optical properties of [001] and [111] poled crystals are very similar,but quite different from those of the [011] poled crystal.     

Temperature-Dependent Sellmeier Equation for 1.0 mol% Mg-Doped Stoichiometric Lithium Tantalate

We propose new coefficients for the Sellmeier equations of 1.0mol% Mg-doped stoichiometric LiTaO3. The extraordinary refractive indices for the wavelength range 0.5-4.0μm and for temperature 30-170℃ are based on measured data derived from quasi-phase-matched （QPM） optical parametric oscillator （OPO） and second- harmonic generation （SHG） based on periodically poled Mg-doped stoichiometric LiTaO3 with a pump wavelength of 1064nm. The corrected refractive indices are in good agreement with our experimental data obtained from QPM OPO and SHG pumped at 1064 μm at different temperatures.     

Accurate measurement of the main refractive indices and thermo-optical coefficients of the calcite crystal

The main refractive indices of calcite crystal are measured by the means of auto-collimation,and the thermo-optical coefficients are calculated.The coefficient expression of SeUmeier equation is obtained by solving Sellmeier equation strictly and the refractive indices of different wavelengths are calculated,which accord with experimental results very well.The measured main refractive indices of calcite at 488-nm wavelength are identical with the values obtained by Sellmeier equation.     

Optical Dispersion Behavior and Band Gap Energy of Relaxor Ferroelectric 0.92Pb（Mgl/3Nb2/3）O3-0.08PbTiO3 Single Crystal

Refractive indices and extinction coefficients of O.92Pb（Mgl/3Nb2/3）O3-O.O8PbTiO~（PMN-O.OSPT） single crystaJ are investigated by variable angle spectroscopic ellipsometry （VASE） at different wavelengths. The parameters relative to the energy band structure are obtained by fitting to the single-oscillator dispersion equation, and the band gap energy is also deduced from the Tauc equation. Similar to most oxygen-octahedra ferroelectries, PMN-O.OSPT has the same dispersion behavior described by the refractive-index dispersion parameters.     

Physical Properties of Novel Lead-Bismuthate Glasses with Large Transmitting Windows

Novel lead-bismuthate glasses with low OH concentration have been obtained in the Bi2O3-PbO-SrO system. The role of the different components in the glass formation has been explored from the density, refractive index measurements, indicating that the physical properties are mainly agected by Bi2O3 and PbO contents. The densities and refractive indices of these glasses are in the ranges of 7.639-7.699 g/cm^3 and 2.47-2.94, respectively. A wide transmitting window from visible to infrared (IR) regions and good thermal stability for some compositions of these g/asses have been observed, which make them appealing candidates for different optical applications suc has upconverting phosphors, new laser materials, optical waveguides and crystal-free fibre drawing.     

Optical properties of hexagonal boron nitride thin films deposited by radio frequency bias magnetron sputtering

The optical properties of hexagonal boron nitride (h-BN) thin films were studied in this paper. The films were characterized by Fourier transform infrared spectroscopy, UV--visible transmittance and reflection spectra. h-BN thin films with a wide optical band gap E_g (5.86 eV for the as-deposited film and 5.97 eV for the annealed film) approaching h-BN single crystal were successfully prepared by radio frequency (RF) bias magnetron sputtering and post-deposition annealing at 970~K. The optical absorption behaviour of h-BN films accords with the typical optical absorption characteristics of amorphous materials when fitting is made by the Urbach tail model. The annealed film shows satisfactory structure stability. However, high temperature still has a significant effect on the optical absorption properties, refractive index n, and optical conductivity σ of h-BN thin films. The blue-shift of the optical absorption edge and the increase of E_g probably result from stress relaxation in the film under high temperatures. In addition, it is found that the refractive index clearly exhibits different trends in the visible and ultraviolet regions. Previous calculational results of optical conductivity of h-BN films are confirmed in our experimental results.     

Period and temperature tuning of cascaded opticalparametric oscillator based on periodically poled LiNbO3

We report the broadly tunable source by a cascaded optical parametric oscillator in the periodically poled LiNbO_3 (PPLN) with domain grating period and temperature tuning. The optical parametric oscillator was pumped by a passive Q-switched Nd:YVO_4 laser. Multi-wavelength outputs from visible to infrared were obtained. The temperature of the PPLN crystal changed within the range of 70－150℃ with different periods of PPLN. The tunable range covered from 433 to 1657nm.     

AN INVESTIGATION FOR THE Cd2+-VACANCIES IN RbCdF3 and CsCdF3 CRYSTALS DOPED WITH Fe3+ IMPURITIES

This paper presents high-order perturbation calculations for the zero-field splitting parameters D, F, and a of Fe³⁺-V_Cd pairs in RbCdF₃ and CsCdF₃ crystals doped with Fe³⁺ impurities. In comparison with experimental data, the present results are better than those obtained in previous work by using the phenomenological su-perposition model of spin-Hamiltonian. Moreover, the crystal fields arising from the Cd²⁺-vacancy and their induced crystal lattice distortion are analysed and calculated. It is found that the contribution from the Cd²⁺-vacancies cannot be ignored. Mena-while, we obtain that a ligand F^- along the [001]-axis moves towards the central Fe³⁺ ion by Δ= 0.0020nm in RbCdF₃ and 0.0028nm in CsCdF₃. These results are quite different from Δ = 0.0104nm and Δ = 0.0112nm, respectively, obtained in previous work by using the superposition model of spin-Hamiltonian and ignoring the effect of the vacancy.     

High efficiency continuous-wave tunable signal output of an intracavity singly resonant optical parametric oscillator based on periodically poled lithium niobate

In this paper we report on a continuous-wave (CW) intracavity singly resonant optical parametric oscillator (ICSRO) based on periodically poled LiNbO₃ (PPLN) pumped by a diode-end-pumped CW Nd:YVO₄ laser. Considering the thermal lens effects and diffraction loss, an optical ballast lens and a near-concentric cavity are adopted for better operation. Through varying the grating period and the temperature, the tunable signal output from 1406~nm to 1513~nm is obtained. At a PPLN grating period of 29~μ m and a temperature of 413~K, a maximum signal output power of 820~mW at 1500~nm is achieved when the 808~nm pump power is 10.9~W, leading to an optical-to-optical conversion efficiency of 7.51%.     

Influence of Concentration of Vanadium in Zinc Oxide on Structural and Optical Properties with Lower Concentration

ZnO films doped with different vanadium concentrations are deposited onto glass substrates by dc reactive magnetron sputtering using a zinc target doped with vanadium. The vanadium concentrations are examined by energy dispersive spectroscopy （EDS） and the charge state of vanadium in ZnO thin films is characterized by x-ray photoelectron spectroscopy. The results of x-ray diffraction （XRD） show that all the films have a wurtzite structure and grow mainly in the c-axis orientation. The grain size and residual stress in the deposited films are estimated by fitting the XRD results. The optical properties of the films are studied by measuring the transmittance. The optical constants （refractive index and extinction coefficient） and the film thickness are obtained by fitting the transmittance. All the results are discussed in relation with the doping of the vanadium.     

Electronic structures and optical properties of Zn-doped β-Ga2O3 with different doping sites

<正>The electronic structures and optical properties of intrinsicβ-Ga₂O₃ and Zn-dopedβ-Ga₂O₃ are investigated by first-principles calculations.The analysis about the thermal stability shows that Zn-dopedβ-Ga₂O₃ remains stable. The Zn doping does not change the basic electronic structure ofβ-Ga₂O₃,but only generates an empty energy level above the maximum of the valence band,which is shallow enough to make the Zn-dopedβ-Ga₂O₃ a typical p-type semiconductor.Because of Zn doping,absorption and reflectivity are enhanced in the near infrared region.The higher absorption and reflectivity of Zn_Ca（2） than those of Zn_Ca（1）are due to more empty energy states of Zn_Ca（2）than those of Zn_Ca（1） near E_f in the near infrared region.     

Effect of Fe concentration on the nonlinear refraction and reverse saturable absorption in ferroelectric X-cut LiNbO_3 crystal

In this Letter, the effects of the iron(Fe) dopant concentration on the nonlinear optical properties of iron-doped ferroelectric X-cut Li Nb O3 crystals plates are studied by using the Z-scan technique with a cw laser at the wavelength of 532 nm. The amount of iron in the compound is varied from 0 to 0.15 mol%. Measurements of nonlinear refractive index n2 and the nonlinear absorption coefficient β are determined. The sign of the nonlinear refractive index is found to be negative and the magnitude is on the order of 10-8cm2∕W. This nonlinear effect increases as the concentration increases from 0 to 0.15 mol%. A good linear relationship is obtained between nonlinear refractive index, nonlinear absorption coefficient, and concentration.     

Ellipsometric analysis and optical absorption characterization of gallium phosphide nanoparticulate thin film

Gallium phosphide (GaP) nanoparticulate thin films were easily fabricated by colloidal suspension deposition via GaP nanoparticles dispersed in N,N-dimethylformamide. The microstructure of the film was performed by x-ray diffraction, high resolution transmission electron microscopy and field emission scanning electron microscopy. The film was further investigated by spectroscopic ellipsometry. After the model GaP+void|SiO₂ was built and an effective medium approximation was adopted, the values of the refractive index n and the extinction coefficient k were calculated for the energy range of 0.75 eV-4.0 eV using the dispersion formula in DeltaPsi2 software. The absorption coefficient of the film was calculated from its k and its energy gaps were further estimated according to the Tauc equation, which were further verified by its fluorescence spectrum measurement. The structure and optical absorption properties of the nanoparticulate films are promising for their potential applications in hybrid solar cells.     

Three-dimensional size and orientation of the precipitates in AZ91 magnesium alloys measured by TEM techniques

Knowledge of the microscopic structure, including three-dimensional (3-D) size and orientation of the precipitates, is essential to fully understand the mechanical properties of the magnesium alloys and designing the alloys with better performance. Analytical TEM with high spatial resolution offers the simultaneous measurements of 3-D size, structure, orientation, composition of the precipitates from one typical sample along an established crystallographic axis. Besides popular Burgers orientation relationship (OR), other ORs such as Pitsch--Schrader OR, Crawley OR, Potter OR and a new OR with the form of [0001]_α 1.0° from [311]_γ and (11\bar 20)_α 2.0° from (03\bar 3)_γ between the magnesium matrix and the precipitate γ -Mg₁₇Al₁₂ are identified by TEM imaging and diffraction techniques. As a case study, the thicknesses of the individual precipitates with Burgers OR are further measured to be 100--200~nm through both electron energy-loss spectroscopy and x-ray energy dispersive spectroscopy combining differential x-ray absorption and extrapolation, which are in agreement with the overall 3-D size statistic distribution results obtained through analysing various samples along various directions. Furthermore, the fabricated wedge-shape structure provides a platform on which to study the dependence of the interfacial strain on the variation of the thickness.     

Synthesis and study the influence of yttrium doping on band structure,optical, non-linear optical and dielectric results for Ca12Al14O33 (C12A7) single crystals grown using traveling-solvent floating zone (TSFZ) method

Ca₁₂Al₁₄O₃₃(C12A7)and Y_0.02Ca_11.98Al₁₄O₃₃(Y-C12A7)single crystals were grown by using the traveling-solvent floating zone(TSFZ)method.The temperature was increased to avoid the bubbles and cracks which may be formed during the preparation of the ingot material.We have started with the flux higher than the normal to avoid the bubbles and make good treatment for the solid-liquid interface.The structures of both Ca₁₂Al₁₄O₃₃(C12A7)and Y_0.02Ca_11.98Al₁₄O₃₃(Y-C12A7)were studied by using x-ray diffraction(XRD).Optical properties for C12A7 and Y-C12A7 single crystals have been studied in order to determine the optical parameters such as optical energy gap(Eg),refractive index n,oscillating energy(Eo),dispersion energy(Ed),volume energy loss function(VELF),and surface energy loss function(SELF).Finally,a new result for these samples is that the third-order nonlinear optical susceptibility(χ(3))was determined.The results have been discussed with effect of Y-doping on the C12A7 single crystals for optical and industrial applications.     

Resonantly pumped Q-switched Er:GdVO4 laser

We describe a Q-switched Er:GdVO₄ laser resonantly pumped by a MgO-doped periodically poled LiNbO₃ optical parametric oscillator （MgO: PPLN OPO） at 1536 nm. In continuous-wave lasing, the maximum output power is 1.14 W with an incident pump power of 4.7 W and a slope efficiency of 27%. In Q-switched operation, 1.1 mJ of output pulse energy is achieved at 200 Hz. The upper-state lifetime at different pulse repetition frequencies is also calculated.     

Effect of Si δ-Doping on the Linear and Nonlinear Optical Absorptions and Refractive Index Changes in InAlN/GaN Single Quantum Wells

In the framework of effective mass approximation,we theoretically investigate the electronic structure of the Si S-doped InAIN/GaN single quantum well by solving numerically the coupled equations Schr(o|¨)dinger-Poisson self-consistently.The linear,nonlinear optical absorption coefficients and relative refractive index changes are calculated as functions of the doping concentration and its thickness.The obtained results show that the position and the amplitude of the linear and total optical absorption coefficients and the refractive index changes can be modified by varying the doping concentration and its thickness.In addition,it is found that the maximum of the optical absorption can be red-shifted or blue-shifted by varying the doping concentration.The obtained results are important for the design of various electronic components such as high-power FETs and infrared photonic devices.     

Optical properties of aluminum-doped zinc oxide films deposited by direct-current pulse magnetron reactive sputtering

A series of （103）-oriented aluminum-doped zinc oxide （AZO） films were deposited on glass substrates via direct- current pulse magnetron reactive sputtering at different O2-to-Ar gas flow ratios （GFRs）. The optical properties of the films were characterized using the fitted optical constants in the general oscillator model （which contains two Psemi-Tri oscillators） through the use of measured ellipsometric parameters. The refractive index dispersion data below the interband absorption edge were analyzed using a single-oscillator model. The fitted optical energy gap obtained using the single- oscillator model clearly shows a blue shift, followed by a red shift, as the GFR increases from 0.9/18 to 2.1/18. This shift can be attributed to the change in the free electron concentration of the film, which is closely related to the film stress. In addition, the fitted β value indicates that the AZO film falls under the ionic class. The pbotoluminescence spectrum indicates a photoluminescence mechanism of the direct and wide energy gap semiconductor.     

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.     

Oscillator strengths for 22S--n2P transitions of the lithium isoelectronic sequence from Z = 11 to 20

The dipole-length, dipole-velocity and dipole-acceleration absorption oscillator strengths for the 1s22s-1s2np (3≤n≤9) transitions of lithium-like systems from Z=11 to 20 are calculated by using the energies and the multiconfiguration interaction wave functions obtained from a full core plus correlation method, in which relativistic and mass-polarization effects on the energy, as the first-order perturbation corrections, are included. The results of three forms are in good agreement with each other, and closely agree with the experimental data available in the literature. Based on the quantum defects obtained with quantum defect theory (QDT), the discrete oscillator strengths for the transitions from the ground state to highly excited states 1s2np (n≥10) and oscillator strength densities corresponding to the bound-free transitions are obtained for these ions.