Search

Herein we present a detailed analysis of the optical response of artificial opal films realized employing a near-field scanning optical microscope in collection and transmission modes. Near-field patterns measured at the rear surface when a plane wave impinges on the front face are presented with the finding that optical intensity maps present a clear correlation with the periodic arrangement of the outer surface. Calculations based on the vector Korringa-Kohn-Rostoker method reproduce the different profiles experimentally observed as well as the response to the polarization of the incident field. These observations constitute the first experimental confirmation of the collective lattice resonances that give rise to the optical response of these three dimensional periodic structures in the high-energy range. [ABSTRACT FROM AUTHOR]

A near-field scanning optical microscope (NSOM) is used to perform structural and optical characterization of the surface layer after Zn diffusion in a channel waveguide fabricated on lithium niobate. A theoretical approach has been developed in order to extract refractive index contrast from NSOM optical transmission measurements (illumination configuration). As a result, different solid phases present on the sample surface can be identified, such as ZnO and ZnNb2O6. They appear like submicrometric crystallites aligned along the domain wall direction, whose origin can be ascribed to some strain relaxation mechanism during the annealing process after Zn diffusion. [ABSTRACT FROM AUTHOR]

Relevant damage features associated with femtosecond pulse laser and swift-ion irradiations on LiNbO3 crystals are comparatively discussed. Experiments described in this paper include irradiations with repetitive femtosecond-laser pulses (800 nm, 130 fs) and irradiation with O, F, Si, and Cl ions at energies in the range of 0.2–1 MeV/amu where electronic stopping power is dominant. Data are semiquantitatively discussed by using a two-step phenomenological scheme. The first step corresponds to massive electronic excitation either by photons (primarily three-photon absorption) or ions (via ion-electron collisions) leading to a dense electron-hole plasma. The second step involves the relaxation of the stored excitation energy causing bond breaking and defect generation. It is described at a phenomenological level within a unified thermal spike scheme previously developed to account for damage by swift ions. A key common feature for the two irradiation sources is a well-defined intrinsic threshold in the deposited energy density Uth required to initiate observable damage in a pristine crystal: Uth≈1.3×104-2×104 J/cm3 for amorphization in the case of ions and Uth≈7×104 J/cm3 for ablation in the case of laser pulses. The morphology of the heavily damaged regions (ion-induced tracks and laser-induced craters) generated above threshold and its evolution with the deposited energy are also comparatively discussed. The data show that damage in both types of experiments is cumulative and increases on successive irradiations. As a consequence, a certain incubation energy density has to be delivered either by the ions or laser photons in order to start observable damage under subthreshold conditions. The parallelism between the effects of laser pulses and ion impacts is well appreciated when they are described in terms of the ratio between the deposited energy density and the corresponding threshold value. [ABSTRACT FROM AUTHOR]

A near-field scanning optical microscope (NSOM) is used for performing structural and optical characterization of the surface layer after Zn diffusion in a channel waveguide fabricated on lithium niobate. An important part of the Zn at the upper layer surface above the channel waveguide is seen such as Zn[Nb.sub.2][O.sub.6] and ZnO nanocrystals having an average size close to 900 nm

This paper presents a study of the behaviour as optical superlattices of periodically poled LiNbO3and LiTaO3crystals using the Scanning Near-field Optical Microscopy (SNOM) technique. The periodic ferroelectric domains were formed either by electric field poling technique or by the “off-centre Czochralski method” during crystal growth. SNOM patterns were recorded in both collective and reflective configuration, simultaneously with surface topography measurement by AFM (Atomic Force Microscopy). It has been found that regardless of the method used to create the domains, a modulation in the SNOM signal intensity is correlated with the ferroelectric domain structure. The maximum intensity of the collected or reflected SNOM light intensity is centred on the negative domains, whereas the minimum intensity is positioned on the positive domains. This result demonstrates that the modulation of the refractive index is related to the domains and not with the wall between them. [ABSTRACT FROM PUBLISHER]

Abstract: This work shows a study of the periodic ferroelectric domains formed in LiNbO3 crystals doped with rare earths by means of scanning near field optical microscopy (SNOM) technique. It has been observed periodic structures associated with ferroelectric domains with an unexpected high value of the optical contrast working under reflectance SNOM mode. From Raman-Nath diffraction patterns, a refractive index modulation of has been calculated. These results were correlated with the ferroelectric periodic domains obtained by the SNOM technique. A light waveguide effects along the ferroelectric domains is suggested to explain the high reflectance contrast observed in SNOM experiments. [Copyright &y& Elsevier]

Purpose: Successful intraocular lens procedures, that is, implantation of accommodating intraocular lenses (A-IOL), require firm engagement of the IOL haptics to the capsular bag. We evaluated the use of photochemical bonding to engage IOL materials to the capsular bag., Methods: Freshly enucleated eyes of New Zealand rabbits were used in two types of photobonding experiments using Rose Bengal (RB) photoinitiation and green light (532-nm) irradiation. First, RB-stained capsular bag strips were photobonded ex vivo to IOL polymer [poly(2-hydroxyethyl methacrylate) pHEMA] strips in an atmosphere of air and of nitrogen. Second, IOLs were implanted intracapsularly and photobonded intraocularly. Irradiation times were between 30 and 180 seconds, and laser irradiance was between 0.25 and 0.65 W/cm(2). The strength of the bonding was tested using a custom-developed uniaxial extensiometry system and the breakage load (the load that caused breakage per bonded area) was calculated., Results: The breakage load of ex vivo capsule-pHEMA bonds increased exponentially with irradiation time, using 0.45 W/cm(2). In air, the average breakage load across all conditions was 1 g/mm(2) and 1.6 times lower than that in a nitrogen atmosphere. Intraocularly, RB-stained IOLs were strongly photobonded to the capsule bag with breakage loads > 0.8 g/mm(2)., Conclusions: Breakage of the photobonded linkage between IOL material and capsular bag required loads substantially greater than the maximum force of ciliary muscle, suggesting that this technology may introduce a new paradigm for engagement of A-IOLs. The bonding produced in air was stronger than that in nitrogen atmosphere, suggesting that oxygen is involved in the chemical mechanism for photobonding.

Alexithymia is a psychological trait characterised by difficulty in perceiving and expressing emotions and body sensations. Failure to perceive dyspnoea could lead alexithymic asthmatics to underestimate the severity of an asthma exacerbation, and thereby increase the risk of developing a fatal or near-fatal asthma (NFA) attack. The objective of the present study was to determine the prevalence of alexithymia in NFA patients and to analyse their clinical characteristics. Alexithymia was assessed using the Toronto Alexithymia Scale in this multicentric prospective observational study. From 33 Spanish hospitals, 179 NFA patients and 40 non-NFA patients, as a control group, were enrolled. There was a higher proportion of alexithymia in the NFA group than in the non-NFA group (36 versus 13%). Patients with NFA and alexithymia were older than the rest of the NFA group, and had a lower level of education, a higher level of psychiatric morbidity, a higher proportion of severe persistent asthma and a greater number of prior very severe asthma exacerbations (49 versus 27%). Alexithymia, severe persistent asthma and a low level of education were identified as independent variables related to repeated very severe asthma exacerbations. The results show that alexithymia is more frequent in near-fatal asthma patients compared to the rest of asthmatics and is associated with recurrent very severe asthma exacerbations.

Setting: Specialised tuberculosis out-patient clinic covering a population of 350 885., Objectives: To compare two techniques, ultrasonic nebuliser (UN) and Venturi-type face mask nebuliser (VFMN), for obtaining sputum in patients suspected of having active pulmonary tuberculosis (PTB) and who cannot expectorate, and to analyse the usefulness and cost of sputum induction with UN in a specialised medical practice., Design: Prospective study from October 1997 until March 2000., Results: Of 94 subjects who completed all tests, at least one sample of sputum was obtained from 89 (95.6%). UN provided adequate samples in 86 (93.4%) and VFMN in 66 (71%), a significant difference (P < 0.001). Among 43 patients diagnosed with active PTB, the diagnosis was confirmed in 39 with the samples obtained by sputum induction. Direct acid-fast bacilli smear was positive in 8 (19%). Direct costs were low and the technique can be performed on the day the patient attends the outpatient clinic., Conclusion: Sputum induction with an ultrasonic nebuliser was well-tolerated, of low cost, allows adequate samples to be obtained in the majority of patients who cannot produce sputum, and was more effective than the Venturi-type face mask.

Peritoneal dialysis solutions containing icodextrin are ideal for providing sustained ultrafiltration during long dwells, and they have replaced high glucose for long dwells in some patients. The biocompatibility of these solutions, especially in regard to glucose degradation products, has not been studied in depth. The object of this study was to compare the effects of commercially available dextrose-containing dialysis solutions to those of icodextrin-containing solutions on fibroblast proliferation in vitro. We measured the effect of solutions on cell growth by exposing murine fibroblasts to pH-adjusted test solutions mixed with culture medium, and by comparing cell growth to growth in culture medium only. No statistical difference was observed in the growth of cells exposed to heat-sterilized Extraneal [7.5% icodextrin (Baxter Healthcare, Deerfield, Illinois, U.S.A.)], heat-sterilized Dianeal [1.5% dextrose (Baxter Healthcare)], or filter-sterilized Dianeal [4.25% dextrose (Baxter Healthcare]. Also, no difference was observed in the growth of fibroblasts exposed to heat-sterilized Extraneal or to filter-sterilized Extraneal, but heat-sterilized Dianeal [4.25% dextrose (Baxter Healthcare)] caused a significant reduction in cell growth. Glucose degradation products (GDPs) are known to contribute to reduced cell growth in vitro. Extraneal had lower levels of the GDP acetaldehyde compared to Dianeal (2.5% or 4.25% dextrose). The results demonstrate enhanced in vitro biocompatibility characteristics for Extraneal, possibly related to low GDP levels in Extraneal.