Fe Crystals Research Articles

Wavelength demultiplexing with layered multiple Bragg gratings in LiNbO_3:Fe crystal

Dense wavelength division multiplexing (DWDM) is an important technology for expanding the capacity of optical network. The optical component based on the superimposed Bragg gratings shows that it can be used as one of advantageous multichannel components because of its excellent angle and wavelength selectivities. An optimized method for recording multiple Bragg gratings for wavelength demultiplexing in optical telecommunication band is proposed to achieve gratings with equal diffraction efficiency. A structure of three layers with twenty four gratings is demonstrated in a LiNbO(3):Fe crystal by employing the optimized recording method. Then an initial wavelength demultiplexing experiment based on the formed gratings is carried out in optical telecommunication C-band. The results obtained by measuring and analyzing the transmitted spectra of the fabricated gratings show that the diffraction efficiencies of the gratings are uniform. It is suggested that this kind of multiple gratings can be used for increasing the number of the demultiplexed wavelengths in recording medium with unit volume for WDM.

Deterministic Phase Encoded Holographic Data Storage Using Lenticular Lens Array

This work presents a novel optical holographic encrypted data storage approach based on a phase encoding multiplexed scheme. In the proposed data storage scheme, patterns to be encrypted are stored holographically in a photorefractive LiNbO3:Fe crystal using a lenticular lens array (LLA) sheet phase-encoded multiplexing. Experimental results reveal that rotating an LLA placed as a phase modulator in the path of the reference beam is a simple but effective method of increasing the phase addresses for holographic memory in a crystal. Combining this rotational multiplexing with two-axis rotating multiplexing provides further data storage and data encryption capacity.

White-Light Nonlinear Photonic Lattices in Self-DefocusingMedia

Using fully incoherent white light emitted from an incandescent lampand amplitude mask, we experimentally investigate the influence ofseveral factors on the fabrication of the lattice in photovoltaicself-defocusing LiNbO3:Fe crystal, the factors include theorientation of the crystalline c axis relative to the principalaxis of the photonic lattice and the filament, the diameter of inputdark spot and the separation of the adjacent input dark spots.Experimental results reveal that the best fabricating condition ofphotonic lattices is that the principal axis of lattice is tilted for45° relative to the crystalline c axis which is parallel to thefilament of the lamp. In addition, it is necessary that the diameter ofthe input dark spot is larger than the half of their separation.

Investigations of the light-induced scattering varied with HfO2 codoping in LiNbO3:Fe crystals

Light-induced scattering in LiNbO3:Fe crystals codoped with different concentrations of HfO2 has been investigated. Unusual behaviors with varied HfO2 codoping are observed and explained. Li vacancies are suggested to be the main contributor to the dark conductivity of the crystal and subsequently to induce the threshold effect of the pump light intensity for the light-induced scattering. High photovoltaic field produced in the crystals is thought to be the cause of the serious light-induced scattering at high pump intensity. As a result, LiNbO3:Fe, Hf crystals exhibit an enhanced ability to suppress the light-induced scattering at moderate pump intensity.

EPR of trivalent iron centers in SrF2: Fe crystals

An orthorhombic paramagnetic Fe3+ ion center (concentration of iron ions is 0.1 at. %) was found using EPR in BaF2: Fe crystals irradiated by x rays. The EPR spectra recorded in the Q range at a temperature T = 77 K exhibit both the fine structure typical of a center with effective spin S = 5/2 and a superhyperfine structure (SHFS) indicating the SHFS interaction of the electronic moment of the center with the nuclear magnetic moments of its six ligands (F− ions). An analysis of the SHFS reveals that this center forms through the replacement of a Ba2+ cation by a Fe2+ cation, which transforms into a Fe3+ (6A1g) cation under x-ray irradiation and shifts into a neutral position along the C2 axis of the cubic coordination shell of the replaced host cation.

Photorefractive scattering of the radiation of a helium-neon laser in lithium niobate crystals

The characteristic time dependence of the angular width of the central spot of photorefractive scattering of the radiation of a low-power helium-neon laser is detected for a LiNbO3:Fe (0.3 wt %) crystal. Changes of the pattern of the central spot of diffusion photorefractive scattering of light have been recorded that accompany multiple irradiation of the crystal (P=1−2 mW, λ=0.6328 µm) and successive thermal annealing for 30 min at a temperature of 473 K.

Magnetic properties of epitaxial Fe films on MnPt/Fe(1 0 0)

Magnetic properties of epitaxial Fe films on MnPt/Fe(1 0 0) were measured using X-ray magnetic circular dichroism (XMCD) and Mott electron spin polarimetry (SP). Surface sensitive secondary electron spin polarization images revealed the magnetization orientation of the Fe overlayers with respect to that of the substrate Fe crystal that was measured with bulk-sensitive XMCD. The magnetic domains of the Fe overlayer are influenced by the substrate magnetic domain structure, giving a clear evidence of the magnetic interaction between the Fe overlayer and the substrate Fe through the antiferromagnetic MnPt film.

Magnetophotorefractive effect of holographic recording in LiNbO3:Fe crystals

An experimental investigation of the magnetophotorefractive effect for different holographic recording configurations is presented. Our results show that the diffraction efficiency of holographic grating strongly depends on the applied magnetic field for each configuration, since the magnetophotorefractive effect induces a change of the electric current. The diffraction efficiencies of the refractive-index gratings decrease markedly for all configurations we investigated. The reason for our results is discussed.

Localization and movement of native interstitials in chlorinated SrCl2:Fe crystals

The formation of the electron trapped Fe+(IV) centre, produced by X-ray irradiation at 80 K and further annealing at temperatures of up to 700 K in chlorinated SrCl2:Fe crystals, has been investigated by Electron Paramagnetic Resonance. Our studies report the transformation of the monoclinic Fe+(III) centre into the axial Fe+(IV) centre above 450 K. The formation of the Fe+(IV) centre is attributed to the presence and thermally activated movement of neighbouring interstitial chlorine and alkali impurity Na+ ions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

New aspects of light‐induced charge transport in potassium tantalate crystals doped by copper and iron

AbstractThe light‐induced charge transport process in as grown and thermally treated in oxygen atmosphere nominally pure KTaO3 (KTO) single crystals and KTO doped by Cu (KTO:Cu) and Fe (KTO:Fe) were studied by electron paramagnetic resonance (EPR). A sizeable increasing of the EPR signal of Cu2+ centers and reducing for Fe3+ centers was observed under UV illumination (365nm) in the oxidized KTO:Cu and KTO:Fe crystals respectively. This effect is considered as a sequence of the light induced charge exchange between Cu+ and Cu2+, and between Fe3+ and Fe2+ centers. Correlation between temperature dependencies of the EPR signals and photoconductivity was found and discussed too. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Atomistic simulations of structure transitions and fracture in Fe and Al single crystals

Atomistic simulations of structure transitions and fracture in Fe and Al single crystals

A method of easy fabrication of 2D light-induced nonlinear photonic lattices in self-defocusing LiNbO3:Fe crystal

Using a Fourier transform method we fabricate experimentally the square and hexagonal two dimensional light-induce nonlinear photonic lattices of over 20×20 segments with different period in self-defocusing LiNbO3:Fe crystal. The experimental setup of this method is very simple, the photonic lattices are quite regular and robust, and the period of the lattice can be dominated easily.

Interaction between Two-Dimensional White-Light PhotovoltaicDark Spatial Solitons

Using fully incoherent white light emitted from an incandescent bulb (aline source) and amplitude mask, we study experimentally theinteraction between two 2D white-light photovoltaic dark spatialsolitons with three different separations (40 μm, 50 μm and60 μm) and arrangement directions (parallel to, perpendicular toand tilted at 45° with respect to the crystalline c axis)propagating in parallel in close proximity in self-defocusingLiNbO3:Fe crystal. Experimental results reveal that a 2Dwhite-light dark soliton pair only experiences attractive forces whentheir mutual separation is sufficiently small (<60 μm), and thedegree of the attraction depends on their mutual separation and theirarrangement direction. When the separation is larger than 60 μm,the interaction is not evident.

Photochromic effect in LiNbO_3: Fe :Co

In this paper, Co(2)O(3) was codoped in LiNbO(3): Fe crystals. It was found that Co codoping can give rise to the strong photochromic effect in LiNbO(3): Fe. Based on the UV-VIS-NIR absorption spectra, photorefractive sensitivities, and EPR results for both virgin and sensitized states of the crystal, the photochromic mechanism in this material was suggested as follows. During sensitization, electrons transfer from O(2-) to Fe(3+) directly while holes are thermally excited from O- into the valence band and then partly trapped by Co(2+), which leads to the darkening of the crystal. In bleaching process, the electrons are excited from Fe(2+) to the conduction band by green light and recombine with the holes on the Co(2+) level. Sensitizing/bleaching experiments were also carried out in LiNbO(3): Fe: Co crystals. Fast sensitization found for this material is beneficial to two-color recording.

ニッケル/鉄(100)界面と銅/鉄(100)界面の最安定構造と密着性に関する第一原理計算

The maintenance of the adhesion of material interfaces is important in many technological fields. In this paper, we performed first principles calculation to understand the stable structure and adhesive strength of metallic material interfaces, Ni layer or Cu layer on Fe(100) surface formed by metal plating. In order to confirm the accuracy of our calculation, we have calculated the total energy and the [100] Young's modulus of Fe, Ni or Cu single crystal, by taking the spin-polarization into account. It was found that the calculated result of the crystal structure and lattice constant of these metals agreed satisfactorily with the values determined by experiments. The calculated [100] Young's modulus of Fe, Ni and Cu was 136.7 GPa, 173.7 GPa and 122.2 GPa, respectively. Furthermore, we have calculated the stable configuration of Ni atoms at Fe(100) surface. Ni atoms take the corresponding position to the bcc structure of Fe (100) substrate. Similar result was obtained for Cu atoms at Fe(100) surface. The stable structure of the interfaces of 5 Ni layer/5 Fe(100) layer was determined, which was supported by TEM analysis of plated Ni layer on Fe(100) surface. The calculation also showed that the strength of adhesion of the Ni/Fe(100) interface stronger than that of the Cu/Fe(100) interface.

Colour centres in [formula omitted]:Fe and [formula omitted]:Cu crystals irradiated by 12C ions

The present work is devoted to the investigation of optical absorption of pure and doped LiNbO 3 (LN) single crystals in the spectral range 5000– 32000 cm - 1 induced under influence of the 12C ions irradiation with energy 4.5 MeV/ u (MeV per nucleon) and a fluence 2 × 10 9 cm - 2 at room temperature. It was found that no remarkable absorption changes occur in pure and Mg-doped LN crystals, but in Fe- and Cu-doped ones. The induced additional absorption in LN:Fe crystals is attributed with Fe ions reducing Fe 3 + → Fe 2 + occurring simultaneously with hole centres formation O - , while only Cu 2 + → Cu + reduction was observed in LN:Cu crystals.

Defect solitons in optically induced one-dimensional photonic lattices in LiNbO3:Fe crystal

We observe experimentally defect solitons with the odd and the even symmetry in one-dimensional optically induced nonlinear photonic lattices in self-defocusing LiNbO3:Fe crystal when a Gaussian probe beam is launched at normal incidence. We find that the odd symmetric defect soliton is stable while the even symmetric defect soliton is unstable.

Growth, structure, and properties of KTiOPO4 crystals doped with iron

A series of iron-doped KTiOPO4 (KTP: Fe) single crystals in which iron substitutes for 0.1–0.3% titanium was grown. The structure of the KTP: Fe crystals was determined, and their dielectric and conducting properties were studied. An X-ray diffraction analysis failed to reveal such asmall amount of Fe+3 ions in titanium octahedral positions of the structure. It was found that an increase in the iron concentration results in a lowering of the symmetry of Ti(1)O6 and Ti(2)O6 octahedra. The splitting of the dielectric anomaly due to the ferroelectric phase transition was explained by the mechanism of incorporation of an impurity into different growth pyramids of the crystals. It was established that the aging of the KTP: Fe crystals leads to changes in the permittivity and electrical conductivity during long storage.

EPR of trivalent iron centers in a BaF2: Fe crystal

EPR of trivalent iron centers in a BaF2: Fe crystal

Structural, electronic, and magnetic properties of bcc iron surfaces

Trends in atomic multilayer relaxations, surface energy, electronic work function, and magnetic structure of several low-Miller-index surfaces of iron are investigated employing density functional theory total energy calculations. The calculated topmost layer relaxations reproduce well the experimental contractions and their variation with the surface crystallographic orientation, and surface roughness. The multilayer relaxation sequences correlate with the reduced coordination in surface layers and can be explained in terms of a simple electrostatic picture. The surface energies scale almost linearly with the surface roughness. They agree well with the experimental surface tensions and show a small anisotropy in agreement with predictions based on measurements for other metals. The equilibrium shape of a bcc Fe crystal is determined and discussed. The work function anisotropy is calculated and rationalized in terms of changes in the valence charge distribution. Significantly increased local magnetic moments of atoms in the surface region are determined. The correlation between the anisotropy of the surface magnetic moments and atomic coordination in the outermost layers is demonstrated to follow a simple rule.