Gain-switched semiconductor lasers with pulsed excitation and optical injection for dual-comb spectroscopy.

In this work we demonstrate the capability of two gain-switched optically injected semiconductor lasers to perform high-resolution dual-comb spectroscopy. The use of low duty cycle pulse trains to gain switch the lasers, combined with optical injection, allows us to obtain flat-topped optical frequency combs with 350 optical lines (within 10 dB) spaced by 100 MHz. These frequency combs significantly improve the spectral resolution reported so far on dual-comb spectroscopy with gain-switched laser diodes. We evaluate the performance of our system by measuring the transmission profile of an absorption line of H13CN at the C-band, analyzing the attainable signal-to-noise ratio for a range of averaging times.

Enhanced optical frequency comb generation by pulsed gain-switching of optically injected semiconductor lasers.

We report on the experimental generation of broad and flat optical frequency combs (OFC) in a 1550 nm laser diode using gain switching with pulsed electrical excitation together with optical injection. The combination of both techniques allows the generation of high-quality OFCs at a repetition frequency of 500 MHz, showing a low-noise optical spectrum with unprecedent features in terms of width (108 tones within 10 dB) and flatness (56 tones within 3 dB) in comparison with those previously reported for this modulation frequency. The influence of the injection conditions on the OFC quality is studied. Using these two techniques, it has been possible to reduce the separation between tones, generating high spectral performance OFCs with a repetition rateof 100 MHz.

Analysis of a random modulation single photon counting differential absorption lidar system for space-borne atmospheric CO2 sensing.

The ability to observe the Earth's carbon cycles from space provides scientists an important tool to analyze climate change. Current proposed systems are mainly based on pulsed integrated path differential absorption lidar, in which two high energy pulses at different wavelengths interrogate the atmosphere sequentially for its transmission properties and are back-scattered by the ground. In this work an alternative approach based on random modulation single photon counting is proposed and analyzed; this system can take advantage of a less power demanding semiconductor laser in intensity modulated continuous wave operation, benefiting from a better efficiency, reliability and radiation hardness. Our approach is validated via numerical simulations considering current technological readiness, demonstrating its potential to obtain a 1.5 ppm retrieval precision for 50 km averaging with 2.5 W average power in a space-borne scenario. A major limiting factor is the ambient shot noise, if ultra-narrow band filtering technology could be applied, 0.5 ppm retrieval precision would be attainable.

High-peak-power pulse generation from a monolithic master oscillator power amplifier at 1.5 µm.

We present an experimental study on the generation of high-peak-power short optical pulses from a fully integrated master-oscillator power-amplifier emitting at 1.5 µm. High-peak-power (2.7 W) optical pulses with short duration (100 ps) have been generated by gain switching the master oscillator under optimized driving conditions. The static and dynamic characteristics of the device have been studied as a function of the driving conditions. The ripples appearing in the power-current characteristics under cw conditions have been attributed to mode hopping between the master oscillator resonant mode and the Fabry-Perot modes of the entire device cavity. Although compound cavity effects have been evidenced to affect the static and dynamic performance of the device, we have demonstrated that trains of single-mode short optical pulses at gigahertz frequencies can be conveniently generated in these devices.

Los estudios prospectivos de pacientes consecutivos con enfermedad tromboembólica venosa no identifican a todos los pacientes en riesgo. Análisis multicéntrico ambispectivo del grupo Contaminatep / Prospective studies of consecutive patients with venous thromboembolic disease fail to identify all patients at risk. Multicenter, ambispective analysis of the Contaminatep Group

INTRODUCCIÓN: nuestro grupo ha comenzado un trabajo para estudiar la relación entre la incidencia de TEP y la contaminación ambiental. Para establecer una relación, es una condición metodológica fundamental contar con todos los casos incidentes en un periodo de tiempo. Por este motivo diseñamos este estudio, para valorar la eficacia de recogida de pacientes consecutivos con TEP. MATERIAL Y MÉTODOS: realizamos un estudio ambispectivo, multicéntrico, de un año de duración. En una primera fase se incluyeron prospectivamente todos los casos que ingresaron con diagnóstico de TEP y posteriormente, de forma retrospectiva, realizamos una revisión de los registros hospitalarios de cada uno de los centros participantes. Así, calculamos la eficacia dividiendo el número de casos incidentes en fase prospectiva por el número total de casos reclutados en ambas fases. RESULTADOS: desde febrero 2012 a febrero 2013 se reclutaron 839 pacientes (440 prospectivamente). El reclutamiento prospectivo presentó una eficacia de detección de TEP del 52,4%, mostrando variabilidad según el centro (29,3 - 100%). Cuando analizamos sólo a los pacientes con TEP agudo sintomático idiopático, la eficacia fue del 59,8 %, con variabilidad según centro (31,7 - 100%). La eficacia de reclutamiento de pacientes con TEP secundario o idiopático fue de 42,1% vs. 59,8%, respectivamente (p < 0,001). CONCLUSIONES: en los estudios prospectivos, el porcentaje de pacientes no diagnosticados no es desdeñable. Los resultados de este estudio nos deben hacer pensar en estrategias adicionales para reclutar pacientes consecutivos de forma correcta, principalmente en aquellos estudios donde la pérdida de pacientes supondría un sesgo a la hora de emitir conclusiones

INTRODUCTION: we are studying the relationship between the incidence of pulmonary embolism (PE) and air pollution, and all symptomatic PE were needed over a period of time to establish a relationship. For this reason we designed this study, to assess the efficacy of collection consecutive patients with PE. METHODS: ambispective, multicenter study, from February 2012 to February 2013. In the first phase, we included prospectively all cases admitted at the hospital with PE diagnosis, and in the second phase, we reviewed retrospectively, hospital records from each participating center. So, we calculate the efficacy by dividing the number of incident cases in prospective phase by the total number of cases recruited in both phases. RESULTS: during one year, 839 patients were recruited (440 prospectively). The prospective recruitment presented a PE efficacy detection of 52.4%, showing variability according to the center between 29.3 to 100%. When we analyzed only patients with idiopathic symptomatic PE, efficacy was 59.8%, with variability according to the center between 31.7 to 100%. The recruitment efficacy of patients with secondary or idiopathic PE was 42.1% vs. 59.8%, respectively (p < 0.001). CONCLUSIONS: A wide percentage of patients can pass up from prospectives studies. The results of this study try to make us think, that we need more strategies to get a good recruit of consecutive patients, especially in those studies where is essential collect all patients