Abstract: Silicon thin films have been prepared on sapphire substrates by pulsed laser deposition (PLD) technique. The films were deposited in vacuum from a silicon target at a base pressure of 10-6?mbar in the temperature range from 400 to 800??C. A Q-switched Nd:YAG laser (1064?nm, 5?ns duration, 10?Hz) at a constant energy density of 2?J?× cm-2 has been used. The influence of the substrate temperature on the structural, morphological and optical properties of the Si thin films was investigated. Spectral ellipsometry and atomic force microscopy (AFM) were used to study the thickness and the surface roughness of the deposited films. Surface roughness values measured by AFM and ellipsometry show the same tendency of increasing roughness with increased deposition temperature.
Abstract: Erbium-doped tellurite glasses in the 60TeO2-20ZnO-20ZnCl2-xErCl3 systems, with erbium concentration between x = 1 and 10 mol%, were prepared and their refractive index and density were measured. Er3+ photoluminescence at 1.5 [mu]m and the corresponding lifetime measurements were performed. A full width at half maximum value of about 53 nm for all the samples and lifetimes ranging between 4.2 and of 2.2 ms were obtained from the comparison of the radiative lifetimes calculated by Judd-Ofelt analysis and the measured lifetimes, quantum efficiency higher than 50% was assessed even in the most doped samples. A quenching concentration for the 1.5 [mu]m emission of about 10% was estimated.
Abstract: Neutron diffraction data with high real-space resolution are reported for an extensive series of cesium germanate glasses with 2, 5, 10, 15, 18, 21, 25, and 30 mol % Cs(2)O, and also for pure GeO(2) in its vitreous, quartz, and rutile forms. The results for pure GeO(2) show that neutron diffraction can clearly identify an increase in the Ge-O coordination number above the tetrahedral value of four. The results for cesium germanate glasses give strong evidence that the Ge-O coordination number rises to a maximum of 4.36 +/- 0.03 for 18 mol % Cs(2)O and then declines. This behavior may be associated with the germanate anomaly in the thermophysical properties. A model is developed for the composition-dependence of the Ge-O coordination number, and according to this model the rise in the coordination number involves the formation of mostly GeO(5) units, rather than GeO(6) units. Our results also show that the low alkali anomaly is a longer range phenomenon, and is not associated with a preference for the formation of nonbridging oxygens for very low alkali oxide content.
Abstract: An expanding body of literature suggests Raman spectroscopy is a promising tool for skin cancer diagnosis and in-vivo tumor border demarcation. The development of an in-vivo diagnostic tool is, however, hampered by the fact that construction of fiber optic probes suitable for Raman spectroscopy in the so-called fingerprint region is complicated. In contrast, the use of the high wave-number region allows for fiber optic probes with a very simple design. We investigate whether high wave-number Raman spectroscopy (2800 to 3125 cm(-1)) is able to provide sufficient information for noninvasive discrimination between basal cell carcinoma (BCC) and noninvolved skin. Using a simple fiber optic probe, Raman spectra are obtained from 19 BCC biopsy specimens and 9 biopsy specimens of perilesional skin. A linear discriminant analysis (LDA)-based tissue classification model is developed, which discriminates between BCC and noninvolved skin with high accuracy. This is a crucial step in the development of clinical dermatological applications based on fiber optic Raman spectroscopy.
Abstract: A series of glasses in the (Ge,Si)O2-Nb2O5-(Na,K)2O system were prepared by melting and casting. Their density and characteristic temperatures were determined by Differential Thermal Analysis (DTA) and their structure was analyzed by infrared and polarized Raman spectroscopies. DTA data have indicated an increased glass thermal stability with the replacement of GeO2 by SiO2. Kramers-Kronig analysis of the infrared specular reflectance data indicated a strong ionic character for the germanosilicate glasses. The Raman spectra of germanosilicate compositions were generally dominated by an intense Boson peak at ~72Â cm-1 and a high frequency, polarised peak at ~880Â cm-1, related to NbO6 octahedra with at least one non-bridging oxygen. The germanosilicate structure appears to be formed by alternating GeO4 tetrahedra and NbO6 octahedra, in addition to SiO4 tetrahedra.
Abstract: Accurate targeting of diseased and healthy tissue has significantly been improved by MRI/CT-based navigation systems. Recently, intraoperative MRI navigation systems have proven to be powerful tools for the guidance of the neurosurgical operations. However, the widespread use of such systems is held back by the costs, the time consumption during operation, and the need for MR-compatible surgical devices. Raman spectroscopy is a nondestructive optical technique that enables real-time tissue identification and classification and has proved to be a powerful diagnostic tool in a large number of studies. In the present report, we have investigated the possibility of distinguishing different brain structures by using a single fiber-optic probe to collect Raman scattered light in the high-wavenumber region of the spectrum. For the Raman measurements, 7 pig brains were sliced in the coronal plain and Raman spectra were obtained of 11-19 anatomical structures. Adjacent brain structures could be distinguished based on their Raman spectra, reflecting the differences in their biochemical composition and illustrating the potential Raman spectroscopy holds as a guidance tool during neurosurgical procedures.
Abstract: In vivo Raman spectroscopy, using fiber-optic probes is hindered by the intense background signal, which is generated in the fused-silica fibers, in the fingerprint region of the Raman spectrum (approximately 0-2000 cm(-1)). Optical filtering is necessary to obtain tissue spectra of sufficient quality. The complexity of fiber-optic probes for fingerprint Raman spectroscopy, in combination with size constraints and flexibility requirements for in vivo use have been a major obstacle in the development of in vivo diagnostic tools based on Raman spectroscopy. A setup for remote Raman spectroscopic tissue characterization in the high-wavenumber region ( approximately 2400-3800 cm(-1)) is presented. It makes use of a single, unfiltered, optical fiber for guiding laser light to the sample and for collecting scattered light and guiding it back to a spectrometer. Such a simple configuration is possible because the fused-silica core and cladding of the fiber present almost no Raman background signal at these wavenumbers. Several commercially available optical fibers were tested with respect to Raman signal background, to determine their suitability for in vivo Raman spectroscopy measurements in the high-wavenumber region. Different fiber core, cladding, and coating materials were tested. Silica core-silica clad fibers, with an acrylate coating and a black nylon jacket, proved to be one of the best candidates. In vitro measurements on brain tissue of a 6-month-old pig were obtained with a remote high-wavenumber Raman setup. They illustrate the low background signal generated in the setup and the signal quality obtained with a collection time of 1 s.
Abstract: Raman spectroscopy is a powerful diagnostic tool, enabling tissue identification and classification. Mostly, the so-called fingerprint (approximately 400-1800 cm(-1)) spectral region is used. In vivo application often requires small flexible fiber-optic probes, and is hindered by the intense Raman signal that is generated in the fused silica core of the fiber. This necessitates filtering of laser light, which is guided to the tissue, and of the scattered light collected from the tissue, leading to complex and expensive designs. Fused silica has no Raman signal in the high wave number region (2400-3800 cm(-1)). This enables the use of a single unfiltered fiber to guide laser light to the tissue and to collect scattered light in this spectral region. We show, by means of a comparison of in vitro Raman microspectroscopic maps of thin tissue sections (brain tumors, bladder), measured both in the high wave number region and in the fingerprint region, that essentially the same diagnostic information is obtained in the two wave number regions. This suggests that for many clinical applications the technological hurdle of designing and constructing suitable fiber-optic probes may be eliminated by using the high wave number region and a simple piece of standard optical fiber.
Abstract: We report on a Raman scattering study of oxy-fluoride glass-ceramics with a typical composition 32SiO2:9AlO1.5:31.5CdF2:18.5PbF2:5.5ZnF2:3.5ErF3 (in mol%), which indicates a narrow size distribution of [beta]-PbF2 fluoride nano-crystals, typically of 13 ± 1 nm, in the silica-based glass network and gives insight on how then nano-crystals are incorporated into the glassy network. The Raman spectra indicate the presence of Q0, Q1 and Q2-like units, which are SiOxF4-x tetrahedra with zero, one and two bridging oxygens, respectively. The frequency, width and depolarization ratio of Raman bands corresponding to these Qn-like units (n=0, 1, 2) indicate that Q0 units are mostly symmetric SiO4 tetrahedra, Q1 are SiO4 tetrahedra where one F may substitute for O and Q2 are SiO4 tetrahedra where one or two F may substitute for O. We argue that the non-bridging O atoms belonging to Qn tetrahedra, mostly to Q0 tetrahedra, are located near the interface between the nano-crystalline and glassy phases, allowing an easy accommodation of fluoride nano-crystals with a spherical shape, in the oxide glass network. This was in agreement with the very low-frequency Raman features found between ~4 and 8 cm-1, due to acoustic vibrations of the nano-crystals embedded in the glassy matrix.
Abstract: Zinc and lead chloro-tellurite glasses are candidates for hosting rare earth ions, due to a rare earth ion solubility as high as 10 mol% and maximum vibrational energies lower than 800 cm-1, combined with a chemical durability superior to that of halide glasses and optical transparency from the visible to the middle infrared. A series of glasses in the TeO2-ZnO-ZnCl2 system, doped with 1-10 mol% ErCl3, were prepared and heat treated in air between 350 and 500 °C. The early stages of the formation of the crystalline phases formed within the TeO2-based glass matrix were determined in situ by time-resolved X-ray powder diffraction, recorded during thermal treatment, using a synchrotron radiation source. Only two crystalline phases, TeO2 and Zn2Te3O8, were identified. Extended X-ray absorption fine structure spectroscopy above the Er LIII edge was used, to characterize the Er3+ environments in these oxyhalide glasses, before and after heat treatment. The presence of erbium was found to affect the crystallisation process, since other crystalline phases were formed, which could not be identified, but which appear to include Er3+ ions.
Abstract: This paper reports on the optical properties of Erbium-doped zinc-tellurite (TeO2---ZnCl2---ZnO) oxyhalide glass waveguides, deposited by reactive pulsed laser deposition (RPLD) on silica substrates. Er3+-doped zinc-tellurite glass (ZT) targets were ablated in oxygen dynamical flow at two different pressure values of 5 and 10Â Pa by ArF excimer laser at the fluence of 3.7Â J/cm2. The waveguiding properties of the deposited films were investigated by the m-line technique. The TE0 mode excitation was used for photoluminescence (PL) and Raman measurements, in order to study the Erbium ion 4I13/2-->4I15/2 transition and structural properties of the deposited films, respectively. Optical band gap and wavelength dependence of the real and imaginary parts of the refractive index were estimated from transmission spectra.
Abstract: Glass ceramics are a known class of polycrystalline ceramic materials, where, depending on the glass matrix and the particular crystalline phases, one can obtain materials with improved mechanical, thermal, electrical or optical properties. The characteristics and applications of optical glass ceramics are reviewed, with particular emphasis on rare-earth-doped transparent glass ceramics for photonics, including the search for new transparent glass ceramic compositions and the development of suitable methods to process such materials into functional devices.
Abstract: Glass formation is reported in systems based on zinc chloride and zinc bromide. The addition of oxide compounds such as As2O5 in small quantities (~ 0.5-1 mol%) is sufficient to stabilize those glass-formers, allowing the synthesis of almost pure vitreous zinc chloride and zinc bromide samples, several milimeters thick, with slow cooling rates. Addition of small amounts (up to 10 mol%) of phosphates, nitrides and sulfides was also investigated, but glass formation did not improve as noticeably as with the oxides. Glass transition and crystallization temperatures for a 99.5ZnBr2-0.5As2O3 glass, for example, are ~ 130 and ~ 200°C, respectively, compared with Tg ~ 65°C and Tx ~ 111°C for a 50ZnBr2-40KI-10BaBr2 (mol%) glass. The infrared cut-off wavelength decreases with increaqsing oxide content but, for oxide levels of 0.5-1 mol%, it is still located at ~ 10 [mu]m. Both infrared and polarized Raman spectra have been recorded for the above glasses.
