Pulsed laser deposition of KNbO₃ thin films

The laser ablation of stationary KNbO3 single crystal targets induces a Nb enrichment of the target surface. In rotated targets this effect is observed only in those areas irradiated with low laser fluence. The composition of the plasma formed close to the target surface is congruent with the target composition; however, at further distances K-deficient films are formed due to the preferential backscattering of K in the plasma. This loss may be compensated for by using K-rich ceramic targets. Best results so far have been obtained with [K]/[Nb] = 2.85 target composition, and crystalline KNbO3 films are formed when heating the substrates to 650 °C. Films formed on (100)MgO single crystals are usually single phase and oriented with the (110) film plane parallel to the (100) substrate surface. (100)NbO may coexist with KNbO3 on (100)MgO. At substrate temperatures higher than 650 °C, niobium diffuses into MgO forming Mg4Nb2O9 and NbO, leading to K evaporation from the film. Films formed on (001) alpha-Al2O3 (sapphire) show the coexistence of (111), (110), and (001) orientations of KNbO3, and the presence of NbO2 is also observed. KNbO3 films deposited on (001)LiNbO3 crystallize with the (111) plane of the film parallel to the substrate surface. For the latter two substrates the Nb diffusion into the substrate is lower than in MgO and consequently the K concentration retained in the film is comparatively larger

Ion beam manipulation of the photorefractive properties of SBN planar waveguides

Photo refractive planar waveguides have been fabricated in cerium doped Strontium Barium Niobate (SrxBa(1-x)Nb2O6 : SBN) single crystals by ion beam implantation. The losses measured were as low as 0.1 dB /cm and 7.0 dB /cm for the TM and TE modes respectively. Subsequent two beam coupling experiments performed on the waveguides showed that, unlike BaTiO3 and KNbO3 waveguides formed by ion beam implantation, the two-beam coupling gain direction did not reverse. The response time had also been reduced by two orders of magnitude

Gain reversal studies in photorefractive waveguides

We report on low-loss photorefractive BaTiO3 H+ implanted waveguides exhibiting reversal of two-beam-coupling gain direction, caused by induced colour centres. The anomalous two-beam-coupling gain has been investigated as a function of the input beam ratio

Two-wave mixing in photorefractive SBN planar waveguides

Planar waveguides have been fabricated in SBN:61 and SBN:75 by ion-beam implantation. The implantation was carried out using 2.0MeV H+ ions with doses ranging from 2x10 for the TE mode. These losses are significantly lower than those observed for planar waveguides fabricated previously using sulphur diffusion [1]. Two beam coupling experiments were then carried out on the SBN waveguide where it was observed that the gain direction was the same as that of the bulk crystal. Previously, in both BaTiO3 [2] and KNbO3 [3] planar waveguides fabricated in the same manner, the gain direction for two beam coupling had been shown to reverse. This phenomenon may be due to the ion beam implantation process reducing the waveguide layer and subsequently changing the ratio of impurity atom oxidation states - in the case of BaTiO3, the ratio of Fe2+:Fe3+. It is thought that the predominant photoexcited charge carrier in both BaTiO3 and KNbO3 is changed from the hole to the electron whereas in SBN, the electron remains the predominant carrier even after the implantation process. Modelling of these effects has been undertaken, giving an explanation of why gain reversal should occur in certain photorefractive planar waveguides fabricated by ion-beam implantation. This paper will discuss the gain and response time of the SBN waveguide in comparison to the bulk and the theoretical predictions of the effects of ion-beam implantation on photorefractive materials

Photorefractive planar waveguides in BaTiO₃ fabricated by ion-beam implantation

For the first time to our knowledge, photorefractive properties have been observed in planar waveguides fabricated by the technique of ion-beam implantation in BaTiO3 single crystals. The implantation was carried out by using 1.5 MeV H+ ions at a dose of 10-16 ions/cm2. For a given input power, a decrease in the effective photo-refractive two-beam coupling response time of ≥102 has been observed, owing to a combination of optical confinement within the waveguide and possible modification of charge-transport properties induced through implantation. Experiments carried out on the two-beam coupling gain show that the gain direction has been reversed in the waveguide compared with that of the bulk crystal

BaTiO₃ waveguide self-pumped phase conjugator

For the first time to our knowledge, self-pumped phase conjugation is reported in a planar waveguide structure in a BaTiO3 single crystal. The waveguide was fabricated by the technique of ion implantation, with 1.5-MeV H+ ions at a dose of 1016 ions/cm2. Phase-conjugate reflectivities >20% have been measured for waveguide self-pumped phase conjugation, and, for a given input power, an order-of-magnitude reduction in the response time is observed in the waveguide compared with the bulk. The fidelity of phase conjugation in the guide is also discussed

Testing "microscopic" theories of glass-forming liquids

We assess the validity of "microscopic" approaches of glass-forming liquids based on the sole k nowledge of the static pair density correlations. To do so we apply them to a benchmark provided by two liquid models that share very similar static pair density correlation functions while disp laying distinct temperature evolutions of their relaxation times. We find that the approaches are unsuccessful in describing the difference in the dynamical behavior of the two models. Our study is not exhausti ve, and we have not tested the effect of adding corrections by including for instance three-body density correlations. Yet, our results appear strong enough to challenge the claim that the slowd own of relaxation in glass-forming liquids, for which it is well established that the changes of the static structure factor with temperature are small, can be explained by "microscopic" appr oaches only requiring the static pair density correlations as nontrivial input.Comment: 10 pages, 7 figs; Accepted to EPJE Special Issue on The Physics of Glasses. Arxiv version contains an addendum to the appendix which does not appear in published versio

Clinical delineation and natural history of the PIK3CA-related overgrowth spectrum.

Somatic mutations in the phosphatidylinositol/AKT/mTOR pathway cause segmental overgrowth disorders. Diagnostic descriptors associated with PIK3CA mutations include fibroadipose overgrowth (FAO), Hemihyperplasia multiple Lipomatosis (HHML), Congenital Lipomatous Overgrowth, Vascular malformations, Epidermal nevi, Scoliosis/skeletal and spinal (CLOVES) syndrome, macrodactyly, and the megalencephaly syndrome, Megalencephaly-Capillary malformation (MCAP) syndrome. We set out to refine the understanding of the clinical spectrum and natural history of these phenotypes, and now describe 35 patients with segmental overgrowth and somatic PIK3CA mutations. The phenotypic data show that these previously described disease entities have considerable overlap, and represent a spectrum. While this spectrum overlaps with Proteus syndrome (sporadic, mosaic, and progressive) it can be distinguished by the absence of cerebriform connective tissue nevi and a distinct natural history. Vascular malformations were found in 15/35 (43%) and epidermal nevi in 4/35 (11%) patients, lower than in Proteus syndrome. Unlike Proteus syndrome, 31/35 (89%) patients with PIK3CA mutations had congenital overgrowth, and in 35/35 patients this was asymmetric and disproportionate. Overgrowth was mild with little postnatal progression in most, while in others it was severe and progressive requiring multiple surgeries. Novel findings include: adipose dysregulation present in all patients, unilateral overgrowth that is predominantly left-sided, overgrowth that affects the lower extremities more than the upper extremities and progresses in a distal to proximal pattern, and in the most severely affected patients is associated with marked paucity of adipose tissue in unaffected areas. While the current data are consistent with some genotype-phenotype correlation, this cannot yet be confirmed

The organizational construction of hegemonic masculinity: the case of the US Navy

This article examines the construction of hegemonic masculinity within the US Navy. Based on life history interviews with 27 male officers, this study explores alternative discourses and identities of officers from three different communities in the Navy: aviation, surface warfare, and the supply corps. Definitions of masculinity are relationally constructed through associations of difference: aviators tend to draw upon themes of autonomy and risk taking; surface warfare officers draw upon themes of perseverance and endurance; and supply officers draw upon themes of technical rationality. Further,these masculinities depend upon various contrasting definitions of femininity. Finally,this article explores a series of contradictions that threaten the secure construction of masculinity within this military culture

The transmission problem on a three-dimensional wedge

We consider the transmission problem for the Laplace equation on an infinite three-dimensional wedge, determining the complex parameters for which the problem is well-posed, and characterizing the infinite multiplicity nature of the spectrum. This is carried out in two formulations leading to rather different spectral pictures. One formulation is in terms of square integrable boundary data, the other is in terms of finite energy solutions. We use the layer potential method, which requires the harmonic analysis of a non-commutative non-unimodular group associated with the wedge