Lilia Coronato Courrol

Growth of LiYF4 crystals doped with holmium, erbium and thulium

Crystals of LiYF 4 (YLF) doped with holmium, erbium, and thulium were successfully grown by the Czochralski technique. The synthesis, growth conditions, and pulsed-laser performance using a LiY 0.555 Er 0.38 Tm 0.06 Ho 0.005 F 4 crystal, are presented.

Study of the most suitable new glass laser to incorporate ytterbium: alkali niobium tellurite, lead fluorborate or heavy metal oxide

Abstract Diode-pumped Yb-doped glass lasers have received considerable attention for applications such as high-power beam production or femtosecond pulses generation. In this paper, we evaluate the laser potential of three different glass families doped with Yb3+: alkali lead fluorborate (PbO–PbF2–B2O3), heavy metal oxide (Bi2O3–PbO–Ga2O3) and niobium tellurite (TeO2–Nb2O5–K2O–Li2O). Spectroscopic properties were studied for the samples and calculations of the minimum laser pump intensity (Imin), saturation fluence (Usat) and the theoretical limit of peak power (Pmax) are also presented. A comparison of laser properties of these three different glasses and their importance is shown and analyzed.

Raman scattering, differential scanning calorimetry and Nd3+ spectroscopy in alkali niobium tellurite glasses

Abstract Alkali niobium tellurite glasses have been prepared and some of their properties measured by differential scanning calorimetry and Raman scattering. The vitreous domain was established in the pseudo ternary phases diagram for the system TeO2–Nb2O5–(0.5K2O–0.5Li2O). Raman scattering shows that for samples in the TeO2 rich part of the phase diagram the vitreous structure is composed essentially of (TeO4) units connected by the vertices, as in the α-TeO2 crystal. The addition of alkali and niobium oxides causes depolymerization to occur with structures composed essentially of (TeO3) and (NbO6) units. Samples with the composition (mol%) 80TeO2–10Nb2O5–5K2O–5Li2O, stable against crystallization, were prepared containing up to 10% mol Nd3+. The addition of this oxide increases the rigidity of the vitreous network shifting characteristic temperatures to higher temperatures. For the 10% Nd3+ sample amorphous phase separation is assumed to exist from the observation of two glass transition temperatures. Spectroscopic properties such as Judd–Ofelt Ωλ intensity parameters, radiative emission probabilities, and induced emission cross sections were calculated. From these results and also from the emission quenching observed as a function of Nd3+ concentration, we suggest that these glasses could be utilized in optical amplifying devices.

Laser development of rare-earth doped crystals

Rare earth doped laser crystals present good optical properties providing most of the solid state lasers available today. In particular, some fluoride crystals are capable of forming solid solution with several rare earth fluorides, allowing one to take full advantage of the energy transfer mechanisms that might occur among them. LiREF4 (RE=rare earth) crystals, for example, are so flexible that in some cases the doping concentration can go up to 100%. The Nd:LiLuF4 (Nd:LuLF) system has a 1047-nm emission bandwidth 25% larger than Nd:YLF, which makes it very promising for laser mode-locked operation. Nevertheless, lutetium compounds are very difficult to obtain, therefore Nd-doped mixed crystals grown from LiF-Y1−xLuxF3 (0<x<1) solid solutions were studied. A new laser medium was obtained for the Nd:LiLu0.5Y0.5F4 crystal, which presents a Nd emission bandwidth close to the Nd:LuLF (1.82 nm). The mode-locked operation in a diode pumped laser system using the KLM technique was performed and pulses of 4.5 ps were readily obtained. It is also shown that the LiGdF4 (GLF) is a promising host for diode pumped high power Nd lasers which require crystals with higher dopant concentrations. Another example is the Ho:LiYF4 (Ho:YLF) laser operating at 2065 nm obtained as a result of concentration optimization of the sensitizers Er and Tm. The optimization was based on a model comprising the various energy transfer mechanisms that take place in these long lived metastable states, heavily dependent on the dopants concentration. As a quasi-four-level system, the Ho concentration must be kept very small (≤0.005 mol%). The laser operation was optimized by the dynamical coupling of pump and laser modes, and by the dopants optical cycle. These optimizations resulted in a CW Ho laser with 2 W output, in a diode pumped system operation.

Spectroscopic properties of lead fluoroborate and heavy metal oxide glasses doped with Yb3

Abstract A new glass of heavy metal oxide (25.0Bi2O3–57.0PbO–18.0Ga2O3 (mol%)) doped with Yb3+ is presented and compared with lead fluoroborate glass (43.5H3BO3–22.5PbCO3–34.0PbF2 (mol%)), also doped with ytterbium. The interest in Yb3+ for laser action and short pulse generation under diode pumping has been reported in the literature. Spectroscopic properties were studied for both glasses doped with 0.5 mol% of Yb2O3. The absorption cross-section of the heavy metal oxide glass is (2.20±0.15)×10−20 cm2 at the absorption peak wavelength of 968 nm and its emission cross-section is (0.75±0.05)×10−20 cm2 at the extraction wavelength of 1012 nm. A fluorescence effective linewidth of 86 nm and a fluorescence lifetime of 0.40 ms were measured. In the case of the lead fluoroborate glass used for comparison, these values change to (2.56±0.18)×10−20 cm2 (absorption cross-section), (1.07±0.08)×10−20 cm2 (emission cross-section at 1022 nm), 60 nm (fluorescence effective linewidth) and 0.81 ms (fluorescence lifetime). Calculations of the minimum pump intensity are also presented. Both have spectroscopic properties for laser applications that are similar to those of other known glasses (phosphate and tellurite laser glasses) used as active laser media. The large emission bandwidth measured for the heavy metal oxide is of interest for tunable lasers.

Time dependence and energy-transfer mechanisms in Tm3+, Ho3+ and Tm3+–Ho3+ co-doped alkali niobium tellurite glasses sensitized by Yb3+

Abstract Glass samples with the composition (mol%) 80TeO2–10Nb2O5–5K2O–5Li2O, stable against crystallization, were prepared containing Yb3+, Tm3+ and Ho3+. The energy transfer and energy back transfer mechanisms in samples containing 5% Yb 3+ –5% Tm 3+ and 5% Yb 3+ –5% Tm 3+ –0.5% Ho 3+ were estimated by measuring the absorption and fluorescence spectra together with the time dependence of the Yb 3+ 2 F 5/2 excited state. A good fit for the luminescence time evolution was obtained with the Yokota–Tanimotos diffusion-limited model. The up-conversion fluorescence was also studied in 5% Yb–5% Tm, 5% Yb–0.5% Ho and 5% Yb–5% Tm–0.5% Ho tellurite glasses under laser excitation at 975 nm. Strong emission was observed from 1 G 4 and 3 F 2 Tm 3+ energy levels in all samples. The 5 S 2 Ho 3+ emission was observed only in Yb3+Ho3+ samples being completely quenched in Yb3+/Tm3+/Tm3+ samples.

Mode-locking operation of Nd:LuYLF

We report mode-locked laser operation of a diode-pumped Nd:Lu:YLiF4 crystal. This new laser material allowed generation of pulses shorter than those obtained from the well-established laser me- dium Nd:YLiF4 in the same experimental configuration. The mode- locking regime was obtained by introducing a very weak acousto-optical modulation with Kerr-lens-induced pulse shaping. A suitable negative value of the intracavity group-velocity dispersion was introduced to en- hance the initiation and stabilization of the regime. Pulses as short as 4.5 ps were readily obtained, without troublesome optimization procedures. To allow comparison with previously reported results for Nd:YLiF4 sys- tems, we review the importance of spatial hole-burning effects in mode- locking operation.

Preparation and optimization of aminolevulinic acid with gold nanoparticles for photothermal and photodynamic therapies applications

The use of gold nanoparticles (AuNps) as the vehicle for 5-Aminolevulinic acid (ALA) delivery for photodynamic and photothermic plasmonic therapies is a promising approach, especially with the recent demonstration that this photosensitizer immobilization on the particle surface improves reactive oxygen species (ROS) formation, increasing its cytotoxicity. Gold nanorods (AuNRs) present an absorption spectrum shifted to 700 nm, within the tissue transparency window, which allows excitation of the nanoparticles situated deeper in the tissues. Here, we describe a new synthesis method that was applied to control the shape of the gold nanoparticles during its synthesis. To obtain ALA:AuNRs, precursor ALA:AuNps were irradiated by ultrashort laser pulses. The variation of the laser parameters such as pulse energy and duration and irradiation time was assessed. The relevant mechanisms are discussed.

Identification of atherosclerosis using aminolevulinic gold nanoparticle assay in fecal specimens

The atheromatous plaques exhibit an accumulation of protoporphyrin IX, or PpIX, which is transferred to the feces. In this work it was associated a precursor of the PpIX, the 5-aminolevulinic acid, ALA, with gold nanoparticles (ALA:AuNps). The objective was verify the possibility to use ALA:AuNPs as a diagnosis agent for atherosclerosis. ALA:AuNps were synthesized mixing ALA with Tetrachloroauric(III) acid in miliQ water solution followed by photoreduction with light from a Xenon lamp. A total of 22 Male New Zealand rabbits were divided into 3 groups: control group (CG) where animals received normal diet, control group with ALA (CGALA ) and Experimental Group with ALA:AuNPs ( EGALAAu ) in which the animals received a diet with 1% cholesterol. Measurements of the emission intensity of extracted porphyrins from the feces in the region between 575 and 725 nm were done. An increase in the feces porphyrin emission after ALA and ALA:AuNPs administration was observed.

Europium-Doped Hydroxyapatite: Influence of Excitation Wavelength on the Eu3+ Luminescence in the Hydroxyapatite

Hydroxyapatite (HA) doped with europium (HAEu) offers the advantage of making the hydroxyapatite a fluorescent biomarker, allowing their imaging through emission in vivo and in vitro tests. Several authors had been based their studies about europium site occupation (CaI and CaII) in hydroxyapatite by the lanthanide ion luminescence, verifying the influence of the method of synthesis and concentration of the dopant ion. In this study HA nanoparticles doped with 1.4 mol% of trivalent europium were synthesized by co-precipitation method and thermal treated at different temperatures (600°C and 1200°C). A careful evaluation of the influence of the excitation wavelength of europium luminescence in the HAEu was performed and it has been verified that both the characteristics transitions of europium, at CaI and CaII sites, and the luminescent intensity are dependent on the excitation wavelength. The non-observance of this fact can lead to erroneous conclusions about the site occupation of europium in hydroxyapatites.