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Latent ultrafast laser-assisted domain inversion in congruent lithium niobate
No full textThe combination of light with external electric fields has been successfully used for the domain engineering of ferroelectric lithium niobate crystals [1,2]. It has been shown that whereby the application of the electric field is delayed with respect to the illumination of the crystal. Furthermore, the local coercive field reduction becomes fixed after the first poling cycle. Hence, the initially illuminated and domain inverted regions will re-invert at lower voltages for subsequent poling cycles. The most significant implication of the latency is the decoupling of the laser illumination and E-field application steps which significantly simplifies the experimental setup and allows for high resolution light patterning, e.g. using a phase mask
Ultraviolet light induced single step all-optical poling in lithium niobate
No full textPrecision-scale engineering of domains in ferroelectric lithium niobate crystals is a subject of extensive research recently due to the numerous applications that this material has in optical telecommunications, nonlinear optics and optical sensing. The fabrication of well-defined periodic domain structures for this range of applications requires a robust method for ferroelectric domain inversion which can achieve the desired spatial ferroelectric domain distributions even on submicron scales. Furthermore, this method must be flexible, repeatable, and easy to apply.So far the most popular method for ferroelectric domain reversal, referred to as E-field poling, involves the application of an external electric field across the two opposite z faces of the crystal at room temperature, Spatially selective ferroelectric domain reversal is achieved by covering one z face with photolithographically patterned photoresist or metal which provides the necessary spatially selective electric field contrast. However, the electric field contrast provided by the patterned photoresist is rather poor and consequently widths of ferroelectric domain produced by this method are limited to greater than a few microns
Design and performance of a ZnSe tetra-prism for homogeneous substrate heating using a CO<sub>2</sub> laser for pulsed laser deposition experiments
No full textWe report on the design and performance of a ZnSe tetra-prism for homogeneous substrate heating using a continuous wave CO2 laser beam in pulsed laser deposition experiments. We discuss here three potential designs for homogenizing prisms and use ray-tracing modeling to compare their operation to an alternative square-tapered beam-pipe design. A square-pyramidal tetra-prism design was found to be optimal and was subjected to modeling and experimental testing to determine the influence of interference and diffraction effects on the homogeneity of the resultant intensity profile produced at the substrate surface. A heat diffusion model has been used to compare the temperature distributions produced when using various different source intensity profiles. The modeling work has revealed the importance of substrate thickness as a thermal diffuser in producing a resultant homogeneous substrate temperature distribution
Ultraviolet laser-induced submicron spatially resolved super-hydrophilicity on single crystal lithium niobate surfaces
Full text linkLithium niobate crystal surfaces become super-hydrophilic after ultraviolet laser irradiation. The crystal surface hydrophilicity, which was assessed by the contact angle of a sessile drop of de-ionised water, was found to undergo a transition from mildly hydrophobic (contact angle, theta[E] < 50°) to a super-hydrophilic state (theta[E] < 5° ). Patterning of the hydrophilicity at the micron and sub-micron range has been achieved by spatially modulating the illuminating laser beam
Direct-writing of inverted domains in lithium niobate using a continuous wave ultra violet laser
No full textThe inversion of ferroelectric domains in lithium niobate by a scanning focused ultra-violet laser beam (lambda = 244nm) is demonstrated. The resulting domain patterns are interrogated using piezoresponse force microscopy and by chemical etching in hydrofluoric acid. Direct ultra-violet laser poling was observed in un-doped congruent, iron doped congruent and titanium in-diffused congruent lithium niobate single crystals. A model is proposed to explain the mechanism of domain inversion
UV radiation-induced surface wetting changes in lithium niobate single crystals
No full textIrradiation of lithium niobate crystal surfaces with UV radiation modifies the wetting properties of the surface which becomes super-hydrophilic. This effect is used for spatially selective attachment of chemical species on the laser exposed areas
UV laser direct writing of ferroelectric domain inverted structures in single crystal lithium niobate
No full textFerroelectric domain engineering in lithium niobate (LN) is a subject of extensive research mainly for the fabrication of quasi-phase-matched (QPM) nonlinear optical devices but also for the improvement of linear devices and microstructuring. The most common method for ferroelectric domain engineering is by the application of an external electric field, higher than the coercive field (E Here we present UV laser induced inhibition of ferroelectric domain inversion where spatially selective preexposure of the +z face of congruent LN samples inhibits domain inversion in this area upon the application of an external electric field. In these experiments the two steps of i) UV illumination and ii) E-field application are separated; the application of the external electric field can take place long after (days-months) after the UV illumination
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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