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In two recent works, the authors have investigated the spectro-temporal properties of the random laser emission from solid state dye-doped powders in picosecond pumping regime. Each emission pulse consists, both above and below threshold, in a collection of narrow peaks of a spectro-temporal width at the theoretical limit (ΔωΔt≅1). The distribution of path lengths traveled inside the diffusive active medium by photons that can be amplified by stimulated emission explains this behavior, as demonstrated by a simple theoretical model developed by the authors. The aim of the present work is, first, to develop an implemented model that does not depend on fitting parameters, and which is compatible with the energetic and spectro-temporal properties of the material; and second, to get knowledge about the spatial properties of the emission. The transverse coherence size of each emitted photon packet has been measured; and in addition, we have shown the existence of spatial fluctuations of the emission of these materials, as our model predicts.

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In a very recent work the spectral and temporal properties of the random laser emission from solid state dye-doped powders have been investigated by the authors in picosecond pumping regime. The emission shows within each pulse, peaks of more intensity than background, and of a spectro-temporal width at the theoretical limit (ΔωΔt≅1), even in conditions well below the threshold. The relationship between the distribution of paths lengths traveled by photons inside the active medium, and the amplification by stimulated emission explains this behavior. The aim of the present work is to propose a simple model that, in addition to explaining these characteristics of the emission, is compatible with the energetic properties of the material. Particularly interesting is the behavior predicted by the model for the emission decay in sub-threshold conditions, as well as its very good fit with the experimental measurements and its comparison with the one found in low dispersive media, that shows the decisive effect of scattering. The set of results is hardly compatible with a mode structure.

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In this work, the spectral and temporal properties of the random laser emission from dye-doped solid state powders are investigated in picosecond pumping regime. Ultrafast time-resolved spectroscopy achieved with a streak-camera has been used to perform a detailed study of the temporal evolution of the spectrum of their single pulses. Under conditions of low population inversion density, it is observed that the detected radiation occurs as isolated peaks with a very narrow spectro-temporally spread (ΔωΔt≅1). This behavior remains under conditions of high population inversion density, suggesting that the underlying physical mechanism that produces the emission is the same whatever the pumping conditions. Measurements carried out by varying the numerical aperture of the detection system show that each detected peak within a single pulse is associated with a photon pack emitted in a random direction and wavelength. The relationship between the distribution of paths lengths done by photons inside the active medium, and the gain explains the observed behavior.

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A new approach to the problem of energy in solid state dye random lasers is presented. The measurements performed in terms of absolute energy show that the slope efficiency depends on the measurement conditions. In particular, in lasers with pumping in the picoseconds range, the result is really different if measured by recording the emission in the same time range or in a longer one (nanoseconds range). In the last case, no energy threshold is observed. A previously developed model has been applied to the solid state dye random laser. It is a rate-equations model, based on a distribution of paths with different lengths, which partially share population inversion. The results of the model are satisfactory and show that the dynamic behavior is pretty similar in solid state dye random lasers and in inorganic powders.

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A new theoretical approach for random lasing of Nd3+doped powders is presented. The model's singularity lies in the fact that it proposes a probability distribution of the stimulated photon paths lengths in the sample, as well as a population inversion shared by different photon paths. The model's predictions satisfactorily compare with the results of laser threshold and absolute input/output energy slope of a real Random Laser. The main novel issue is that the best fit to the experimental results requires considering a high level of shared population inversion among different paths. The model simulation of local and spatially integrated Random Laser emissions, as well as their time evolution, is in accordance with the experimental behavior. These results also provide a new method of measuring the stimulated emission cross-section in this kind of random laser materials.

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This work presents an overview of near infrared random lasing emitters based on a variety of neodymium (Nd3+)-doped crystal powders with different Nd3+ concentrations and different grain sizes. The pump-configuration used allows for an absolute measurement of both pumping and emitted energies. The results provide an absolute measure of the random laser efficiency and prove a relation of direct proportionality between the absorbance of the material and the laser slope efficiency. Likewise, they suggest a relationship close to an inverse proportionality between the absorbance and the threshold energy per unit area. The temporal behavior of the random laser emission shows noteworthy differences between local and spatially integrated registers.

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Laser slope and threshold properties have been investigated in Nd stoichiometric crystal powders as a function of pump wavelength and pump beam size. Above a given pumped area, the laser slope and the threshold pump energy per unit area are invariant and the known theoretical expressions are well fulfilled. Likewise, the size of the stimulated emission zone as a function of the pump beam area has been measured, also showing a different behavior above or below a given pumped area value which coincides with the one mentioned above. In conclusion, two different operating regimes with different performances are clearly observed as a function of the pump beam area.

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The temporal dynamics of random laser emission from Nd-doped crystal powders has been investigated by using an improved detection device. The precise conditions to detect high contrast, fast oscillations are described. The measured period is about one order of magnitude shorter than the one given in the literature for relaxation oscillations in these materials. The origin of these differences is discussed.

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In this work we present, for the first time to our knowledge, laser emission under wavelength selective laser-pulsed pumping in Nd(3+)-doped TeO(2)-ZnO-ZnF(2) bulk glass for two different Nd(3+) concentrations. The fluorescence properties of Nd(3+) ions in this matrix which include, Judd-Ofelt calculation, stimulated emission cross-section of the laser transition and lifetimes are also presented. The site-selective emission and excitation spectra along the (4)I(9/2)→(4)F(3/2) absorption band show the inhomogeneous behaviour of the crystal field felt by Nd(3+) ions in this fluorotellurite glass which allows for spectral tuning of the laser output pulse as a function of the pumping wavelength. The emission cross-section obtained from the Judd-Ofelt analysis and spectral data (4.9x10(-20) cm(2)) is in fairly good agreement with the value obtained from the analysis of the laser threshold data (4x10(-20) cm(2)).

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The influence of the host matrix on the spectroscopic and laser properties of Nd(3+) in a K-Ba-Al phosphate glass has been investigated as a function of rare-earth concentration. Site-selective time resolved laser spectroscopy and stimulated emission experiments under selective wavelength laser pumping show the existence of a very complex crystal field site distribution of Nd(3+) ions in this glass. The peak of the broad stimulated (4)F(3/2)→(4)I(11/2) emission shifts in a non monotonous way up to 3 nm as a function of the excitation wavelength. This behavior can be explained by the relatively moderate inter-site energy transfer among Nd(3+) ions found in this system and measured by using fluorescence line narrowing spectroscopy. The best slope efficiency obtained for the laser emission was 40%.

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Room temperature random lasing action is demonstrated for the first time in a low concentrated neodymium doped vanadate crystal powder. Laser threshold and emission efficiency are comparable to the ones obtained in stoichiometric borate crystal powders. The present investigation provides a complete picture of the random lasing characteristics of Nd-doped vanadate powder both in the spectral and temporal domain, together with a simplified model which accounts for the most relevant features of the random laser.

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Objetivo: Obtener un estimador de la eficacia del racecadotrilo en el tratamiento de la diarrea aguda mediante revisión sistemática y metaanálisis. Material y métodos: Se seleccionaron ensayos clínicos de calidad realizados en niños en los que se compara la eficacia del racecadotrilo frente a placebo en cuanto a duración de los síntomas, cantidad de deposiciones y efectos secundarios. La búsqueda se ha realizado en bases electrónicas (Med-line, EMBASE, CENTRAL, CINAHL, mRCT, Pascal), en las referencias de los artículos recuperados y mediante contacto con el fabricante, hasta diciembre de 2007. Dos evaluadores independientes han evaluado la calidad. Resultados: Se seleccionaron dos ensayos de muestra pequeña (135 y 172 niños, todos hospitalizados) y de calidad media. Éstos incluyen a niños de edades comprendidas entre 3 meses y 4 años con diarrea aguda de menos de 5 días de evolución a quienes al tratamiento habitual se añade racecadotrilo o placebo. No existen diferencias en la proporción de niños enfermos al quinto día (riesgo relativo [RR] = 0,73; intervalo de confianza [IC] del 95 %, 0,29-1,81). Se demuestra una eficacia leve en el volumen de las deposiciones en las primeras 48 h (diferencia estandarizada de medias [DEM] = -0,65; IC 95 %, -0,88 a -0,42). No se observan diferencias en los efectos secundarios (vómitos, RR = 1,16; IC 95 %, 0,64-2,12). Conclusión: La proporción de curados al quinto día no mejora añadiendo racecadotrilo al tratamiento habitual, si bien disminuye el volumen de deposiciones en las primeras 48 h. Sería interesante estudiar la eficacia en atención primaria valorando el número y volumen de las deposiciones y la duración y número de ingresos (AU)

Objective: To estimate, through a systematic review of the literature, the efficacy of racecadotril in the treatment of acute diarrhoea. Material and methods: Randomised trials carried out in children comparing racecadotril with placebo in terms of diarrhoea recovery, stools output and adverse effects were selected. Electronic databases (Medline, EMBASE, CENTRAL, CINAHL, mRCT, Pascal) and bibliographies of retrieved articles were searched, and the drug developer was contacted. Two authors independently assessed the quality of the retrieved articles and extracted the data. Results: Two small sample size randomised trials (135 and 172 children) of moderate quality were selected. They included children with less than five days diarrhoea and aged between 3 months and 4 years. There was no difference in the proportion of children who recovered by day 5 (RR = 0.73, CI95 % 0.29 to 1.81), although the stools volume during the first 48 hours was less in the racecadotril group (SMD = -0.65, CI95 % -0.88 to -0.52). There is no difference in the risk of vomiting (RR = 1.16, CI95 % 0.64 to 2.12). Conclusion: The proportion of recoveries by the 5th day is the same, although the stool volumes during the first 48 hours are less in the racecadotril treated children. It would be interesting to study the efficacy in a primary care setting assessing the cure rate, the stool volumes and the admission rate to elucidate if there is room for this drug (AU)

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In this work we present a detailed study about the influence of the host matrix in the spectroscopic and laser properties of Nd3+ in three different fluoride glasses. Site-selective time-resolved techniques have been used to investigate the crystal field changes felt by the Nd3+ ion as a consequence of glass inhomogeneity. Stimulated emission experiments performed under selective wavelength laser pumping show the existence of bichromatic emission from two distinguishable site distributions for Nd3+ in fluoride glasses. This result can be explained by the moderate inter-site energy transfer among Nd3+ ions found in these systems.

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OBJECTIVE: To estimate, through a systematic review of the literature, the efficacy of racecadotril in the treatment of acute diarrhoea. MATERIAL AND METHODS: Randomised trials carried out in children comparing racecadotril with placebo in terms of diarrhoea recovery, stools output and adverse effects were selected. Electronic databases (Medline, EMBASE, CENTRAL, CINAHL, mRCT, Pascal) and bibliographies of retrieved articles were searched, and the drug developer was contacted. Two authors independently assessed the quality of the retrieved articles and extracted the data. RESULTS: Two small sample size randomised trials (135 and 172 children) of moderate quality were selected. They included children with less than five days diarrhoea and aged between 3 months and 4 years. There was no difference in the proportion of children who recovered by day 5 (RR=0.73, CI 95% 0.29 to 1.81), although the stools volume during the first 48 hours was less in the racecadotril group (SMD=-0.65, CI 95% -0.88 to -0.52). There is no difference in the risk of vomiting (RR=1.16, CI 95% 0.64 to 2.12). CONCLUSION: The proportion of recoveries by the 5th day is the same, although the stool volumes during the first 48 hours are less in the racecadotril treated children. It would be interesting to study the efficacy in a primary care setting assessing the cure rate, the stool volumes and the admission rate to elucidate if there is room for this drug.

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