C. Sada

Damage effects produced in the near-surface region of x-cut LiNbO3 by low dose, high energy implantation of nitrogen, oxygen, and fluorine ions

The damage effects produced in the near-surface region of x-cut LiNbO3 by low dose, high energy implantation of carbon, nitrogen, oxygen, and fluorine ions are investigated as a function of the dose and substrate temperature during the implant process. The damage profiles were obtained by the Rutherford backscattering RBS-channeling technique, whereas the compositional profiles were performed by secondary ion mass spectrometry. The experimental results showed that the mechanisms governing the damage formation at the surface are strongly connected to the interaction of defects produced when the electronic energy loss exceeds a given threshold close to 220 eV/A. In particular, we observed a damage pileup compatible with a growth of three-dimensional defect clusters.

Room-temperature 1.54 μm photoluminescence from Er-doped Si-rich silica layers obtained by reactive magnetron sputtering

Er-doped Si-rich silica layers were obtained by reactive magnetron sputtering and both structural and room-temperature photoluminescence properties were investigated. The controlled introduction of hydrogen in the plasma was found to play a critical role in the microstructure and distribution of the Si nanograins formed after annealing. Concomitant density increase and size decrease of these nanograins mostly amorphous were noticed upon increasing the hydrogen partial pressure in the plasma. This was accompanied by a systematic enhancement of the Er emission indicating that both crystallized and amorphous silicon nanoparticles are similarly efficient sensitizers for Er emission. The lifetime of the latter was found as high as 5–6 ms.

Copper doping of silicate glasses by the ion-exchange technique: A photoluminescence spectroscopy study

Copper–alkali ion exchange is used for doping superficial layers of different silicate glasses (commercial soda-lime and BK7) with copper ions. Spectroscopic and time-resolved photoluminescence properties of the obtained systems are studied in the range of 80–294 K. Analysis indicates the presence of Cu+ ions located in distorted octahedral sites, and a different position of the triplet electronic levels for the two glass matrices. The luminescence decay-time signal is simulated by a biexponential behavior, interpreted on the basis of a four-level scheme.

Refractive index dependence of the absorption and emission cross sections at 1.54μm of Er3+ coupled to Si nanoclusters

Absorption coefficient (αabs) of Er3+ ions coupled to Si nanoclusters (Si-nc) in SiO2 has been determined by optical transmission measurements in rib-loaded waveguides characterized by different refractive indices, thus gauging an Er3+ absorption cross section (σabs) of 0.4–1.2×10−20cm2 at 1534nm. Although no significant enhancement due to the presence of Si-nc was observed, a clear dependence on the refractive index has been found. Measurements of the decay lifetime permit one to model the behavior as due to both local and mean field variations caused by the composite nature of the core waveguide layer.

On the dynamics of the damage growth in 5 MeV oxygen-implanted lithium niobate

The damage induced by 5 MeV oxygen ion implantation in x-cut congruent LiNbO3 has been investigated by Rutherford backscattering spectrometry channeling technique. The dynamics of the damage growth has been described by an analytical formula considering the separate contributions of nuclear and electronic energy deposition. It has been hypothesized that the nuclear damage provides the localization of the energy released to the electronic subsystem necessary for the conversion into atomic displacements. The strong influence of the preexisting defects on the damage pileup, foreseen by the analytical formula, has been experimentally verified by pre-implanting the samples with 500 keV oxygen ions. It has been shown that a subsequent 5 MeV oxygen implantation step gives rise to an impressive damage accumulation, eventually leading to the total amorphization of the surface, even at moderate fluences.

Etching effect on periodic domain structures of lithium niobate crystals

Abstract In order to improve the knowledge of the domain structure in LiNbO 3 crystals, the effect of the etching process with HFxa0:xa0HNO 3 (1xa0:xa02 by vol.) has been studied. It has been found, by analyzing the superficial composition with the secondary ion mass spectrometry technique, that during the etching treatment, the fluorine ion diffuses into the crystal, mainly along the positive ferroelectric domain.

Erbium doping of LiNbO3 by the ion exchange process

Erbium-doped LiNbO3 slides are fabricated by the ion exchange process. Compositional in-depth profiles of the species involved in the exchange are obtained by secondary ion mass spectrometry. Spectroscopic properties of Er3+ ions in the matrix are determined by photoluminescence spectroscopy. Structural and spectroscopic analyses suggest the formation of two different microstructures in the exchanged region. The potential of ion exchange for a controlled doping of LiNbO3 is outlined.

Luminescence-induced photorefractive spatial solitons

We report the observation of spatial confinement of a pump beam into a photorefractive solitonic channel induced by luminescence [luminescence induced spatial soliton (LISS)]. Trapped beams have been obtained in erbium doped lithium niobate crystals at concentrations as high as 0.7 molu2009% of erbium. By pumping at 980 nm, erbium ions emit photons at 550 nm by two-step absorption, wavelength which can be absorbed by lithium niobate and originates the photorefractive effect. The luminescence at 550 nm generates at the same time the solitonic channel and the background illumination reaching a steady-state soliton regime.

Characterization of alpha-phase soft proton-exchanged LiNbO3 optical waveguides.

Waveguides in LiNbO3 are realized by a soft proton exchange (SPE) process with use of a melt of stearic acid highly diluted by lithium stearate. No phase transitions are formed when alpha-phase waveguides are obtained by SPE. The alpha-phase presents the same crystalline structure as that of pure LiNbO3 crystal, and it maintains the excellent nonlinear and electro-optical properties of the bulk material. The kinetics of the SPE method is studied by the use of secondary-ion mass spectrometry and prism-coupling techniques. The hydrogen effective diffusion coefficient as well as the self-diffusion coefficients of H+ and Li+ ions are determined as a function of the proton-exchange temperature for X-cut LiNbO3.

Lithium niobate crystals doped with iron by thermal diffusion: Relation between lattice deformation and reduction degree

We report, to our knowledge for the first time, on the experimental observation that the maximum lattice deformation induced at the surface of iron doped lithium niobate crystal by thermal diffusion depends on both the Fe concentration and the reduction degree of the doped layer itself. By exploiting a simple linear model, we suggest a description of this experimental evidence and we point out a procedure that allows the characterization of the in-depth profile of the [Fe2+]/[Fe3+] ratio.