In this work is presented a study on the surface microdomain formation in quasi-SLN Z-cut 3" crystals, with an accurate control on both the composition and on the wafering process. The UV absorption edge has been measured and correlated with the crystal composition, showing the edge shift towards shorter wavelengths. The coercive field has been measured as a function of temperature and it has been found lower in the quasi-SLN substrate if compared with the congruent crystals. The microdomain formation at wafer level can be controlled and avoided by appropriate composition choice as well as wafer mechanical and thermal treatments, and is checked by chemical etching and subsequent optical inspection. It has been found that quasi-SLN crystals with 49.82 Li2O mol% content could present microdomains formation even after the photoresist process. On the other side, quasi-SLN crystals with 49.72 Li2O mol% content seem to be more stable for both photoresist and Ti diffusion process for waveguide fabrication. A careful control on LiNbO3 composition and wafer surface quality allows one to find the proper compositional window for the realization of various advanced optical and electro-optical devices.
Various material and functional properties have been measured in lithium niobate crystals (LiNbO3) with different compositions, starting from conventional congruent composition, up to off-congruent and quasi-stoichiometric ones. The UV absorption edge has been measured and correlated with the crystal composition, showing the edge shift towards shorter wavelengths. The ferroelectric transition Curie temperatures have been determined by differential scanning calorimetry, and it increases with Li2O content in the crystal. The surface composition has been checked by micro-Raman spectroscopy. A narrowing of the linewidths has been observed for quasi-stoichiometric crystal, showing an ordered structure, if compared with congruent composition. The coercive field has been measured as a function of temperature for two different crystal compositions, and it has been found lower in the off-congruent substrate. The Ti-indiffusion process has been studied and compared in congruent and off-congruent LiNbO3 substrates by secondary ion mass spectrometry. The main diffusion process parameters have been determined. The Ti diffusion process has been found considerably slower in off-congruent substrates, if compared with conventional congruent LiNbO3, and resulted almost isotropic. The Li-outdiffusion phenomenon has been observed and correlated wit the Ti concentration profile. A careful control on LiNbO3 composition and material properties allows one to find the proper compositional window for the realization of various advanced optical and electro-optical devices.
The problem of spatial localization of a near-infrared (NIR) light absorber in turbid media is approached using continuous wave (CW) laser diode sources. The excitation and backscattered light are fiber optic guided. It is a preliminary study for the development of simple and portable optical instrumentation concerning quantitative non invasive oxymetry. A stable, not expensive, well defined and reproducibile phantom to test the performances of NIR spectroscopy instrumentation is presented. lntralipid solution is used as turbid medium. The concentration of Intralipid is chosen to match the "in-vivo" optical coefficients. The size distribution of scattering particle are actually determined by a laser light-scattering analyzer. A moving absorber driven by a micrometer positioning system is placed inside the turbid medium. A NIR CW laser diode oxymeter with fiber optic probe is tested with the system. Several measurements are presented at differem source-detector distances, absorber positions and lntralipid concentrations. The maximum inspection depth (MID) is defined and measured for the instrument under test.
A time-gated fluorescence imaging technique was applied on tumor-bearing porphyrin-treated mice to study the sensitizer distribution in different organs and tissue types, and to establish whether false positives in the diagnosis of tumors (based on porphyrin fluorescence) could be generated by this localization in healthy tissues. Mice were administered 25 mg/kg body weight (b.w.) of HpD or 5 mg/kg b.w. of PII, and sacrificed 8 hr later. Time- gated fluorescence images were acquired from tumor, skin, muscle, fat, brain, heart, lung, lymph nodes, liver, bowel, spleen, and bone of both treated and untreated animals. Similar results were obtained with HpD and PII. The presence of porphyrins clearly helps the localization of the neoplastic area, which is characterized by the strongest fluorescence in delayed images. An appreciable long-living emission was observed also in bones. With the exception of the bowel, the fluorescence of other organs was weaker and, in untreated mice, short-living.
After a brief review of the static and dynamic light scattering theory from large particles, an experimental situation of a vesicle distribution in equilibrium with large aggregates is presented. It is shown that light scattering results in this complicated situation can be properly interpreted only if dynamic data are combined with absolute intensity measurements.
Conference Committee Involvement (2)
Manufacturing LEDs for Lighting and Displays
10 September 2007 | Berlin, Germany
Workshop on Photonic Components for Broadband Communication
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