100,430 research outputs found
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
UV laser-assisted fabrication of ridge waveguides in lithium niobate crystals
No full textWe present a UV laser-assisted method for the fabrication of ridge waveguides in lithium niobate. The UV laser irradiation step provides the refractive index change required for the vertical light confinement in the waveguide and also defines the ferroelectric domain pattern which produces the ridge structures after chemical etching
Letter, [Author unclear] to Paulina T. Merritt
No full textHandwritten letter to Paulina Merritt from an unknown author, October 1, 1876.
Light-assisted domain engineering, waveguide fabrication and microstructuring of lithium niobate
No full textThe thesis is focussing on the interaction of lithium niobate with UV and ultrafast laser radiation to achieve 1) ferroelectric domain inversion, 2) waveguide fabrication, and 3) surface microstructuring. Preferential ferroelectric domain inversion has been demonstrated by 'latent light-assisted poling' and 'inhibition of poling' using ultrafast laser irradiation at 400 nm and CW highly absorbed UV radiation (305..244 nm) respectively. The characteristics of the resultant domains have been experimentally investigated as a function of the fabrication conditions and a theoretical model have been proposed to explain the experimental observations. UV radiation in the 305 nm to 244 nm range have been used for the fabrication of optical waveguides in lithium niobate. The waveguiding characteristics and electro-optic response of the UV written optical channel waveguides have been investigated experimentally. Inhibition of poling and post processing has been used for the fabrication of ridge waveguide structures with enhanced refractive index change. Finally, a method for the fabrication of ultra-smooth lithium niobate single crystal photonic microstructures has been proposed. The method is based on surface tension reshaping of surface microstructures which are produced by preferential poling and subsequent etching. Whispering gallery mode resonators have been fabricated and characterised here
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
Laser crystallisation of semiconductor core optical fibres
No full textA laser annealing technique is used to crystallise the core of an amorphous silicon optical fibre. The core of the resulting fibre has high material quality and its optical transmission losses are dramatically reduced
Handwritten biographical information on Paulina T. McClung Merritt
No full textA handwritten biography of Paulina T. McClung Merritt by an unknown author, 1892.
Heterogeneous and tissue-specific regulation of effector T cell responses by IFN-gamma during Plasmodium berghei ANKA infection.
No full textIFN-γ and T cells are both required for the development of experimental cerebral malaria during Plasmodium berghei ANKA infection. Surprisingly, however, the role of IFN-γ in shaping the effector CD4(+) and CD8(+) T cell response during this infection has not been examined in detail. To address this, we have compared the effector T cell responses in wild-type and IFN-γ(-/-) mice during P. berghei ANKA infection. The expansion of splenic CD4(+) and CD8(+) T cells during P. berghei ANKA infection was unaffected by the absence of IFN-γ, but the contraction phase of the T cell response was significantly attenuated. Splenic T cell activation and effector function were essentially normal in IFN-γ(-/-) mice; however, the migration to, and accumulation of, effector CD4(+) and CD8(+) T cells in the lung, liver, and brain was altered in IFN-γ(-/-) mice. Interestingly, activation and accumulation of T cells in various nonlymphoid organs was differently affected by lack of IFN-γ, suggesting that IFN-γ influences T cell effector function to varying levels in different anatomical locations. Importantly, control of splenic T cell numbers during P. berghei ANKA infection depended on active IFN-γ-dependent environmental signals--leading to T cell apoptosis--rather than upon intrinsic alterations in T cell programming. To our knowledge, this is the first study to fully investigate the role of IFN-γ in modulating T cell function during P. berghei ANKA infection and reveals that IFN-γ is required for efficient contraction of the pool of activated T cells
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