Javier Abreu-Afonso

Alignment-free, all-spliced fiber laser source for CARS microscopy based on four-wave-mixing

An environmentally-stable low-repetition rate fiber oscillator is developed to produce narrow-bandwidth pulses with several tens of picoseconds duration. Based on this oscillator an alignment-free all-fiber laser for multi-photon microscopy is realized using in-fiber frequency conversion based on four-wave-mixing. Both pump and Stokes pulses for coherent anti-Stokes Raman scattering (CARS) microscopy are readily available from one fiber end, intrinsically overlapped in space and time, which drastically simplifies the experimental handling for the user. The complete laser setup is mounted on a home-built laser scanning microscope with small footprint. High-quality multimodal microscope images of biological tissue are presented probing the CH-stretching resonance of lipids at an anti-Stokes Raman-shift of 2845 cm(-1) and second-harmonic generation of collagen. Due to its simplicity, compactness, maintenance-free operation, and ease-of-use the presented low-cost laser is an ideal source for bio-medical applications outside laser laboratories and in particular inside clinics.

Estudio comparativo de las partículas en aire ambiente en pacientes ingresados por insuficiencia cardiaca y síndrome coronario agudo

INTRODUCTION AND OBJECTIVES Currently air pollution is considered as an emerging risk factor for cardiovascular disease. Our objective was to study the concentrations of particulate matter in ambient air and analyze their relationship with cardiovascular risk factors in patients admitted to a cardiology department of a tertiary hospital with the diagnosis of heart failure or acute coronary syndrome (ACS). METHODS We analyzed 3950 consecutive patients admitted with the diagnosis of heart failure or ACS. We determined the average concentrations of different sizes of particulate matter (<10, <2.5, and <1 μm and ultrafine particles) from 1 day or up to 7 days prior to admission (1 to 7 days lag time). RESULTS There were no statistically significant differences in mean concentrations of particulate matter <10, <2.5 and <1 μm in size in both populations. When comparing the concentrations of ultrafine particles of patients admitted due to heart failure and acute coronary syndrome, it was observed that the former had a tendency to have higher values (19 845.35 ± 8 806.49 vs 16 854.97 ± 8005.54 cm⁻³, P <.001). The multivariate analysis showed that ultrafine particles are a risk factor for admission for heart failure, after controlling for other cardiovascular risk factors (odds ratio=1.4; confidence interval 95%, from 1.15 to 1.66 P=.02). CONCLUSIONS In our study population, compared with patients with ACS, exposure to ultrafine particles is a precipitating factor for admission for heart failure.

Continuously Tunable Microwave Photonic Filter Using a Multiwavelength Fiber Laser

A tunable microwave photonic filter is demonstrated by employing a stable multiwavelength erbium-doped fiber laser and a dispersive medium. The specific configuration of the multiwavelength laser allows for adjustment of the number of laser lines, i.e., the optical taps of the filter and their spectral spacing. The transfer function of the filter is continuously tunable, exhibiting transmitted bands of less than 1-GHz bandwidth and sidelobe suppression of -17 dB in the 10-30 GHz frequency range.

Relación entre exposición a corto plazo a dióxido de azufre atmosférico y lesiones obstructivas en el síndrome coronario agudo

BACKGROUND AND OBJECTIVES Urban air pollutants are composed of a heterogeneous mixture of substances in gas and aerosol states. The aim of this study was to compare the effects caused by exposure to contaminants in the gas phase and atmospheric particles in ambient air in patients hospitalized for acute coronary syndrome (ACS) regarding the presence or absence of significant obstructive lesions (SOL) in epicardial coronary arteries. PATIENTS AND METHODS Prospectively analyzed a total of 2,110 patients with a diagnosis of ACS. We determined the mean concentrations of contaminants in the gas phase and atmospheric particles from the day before until 7 days prior to admission (1 to 7 days lag time). We divided the study population into those with presence or absence of SOL. RESULTS Of the 2,110 patients with ACS, 1,892 presented SOL and 218 without SOL. When comparing the concentrations of contaminants in the gas phase, we observed that the sulfur dioxide in patients with SOL had a trend toward higher values (10.93 ± 8.33 versus 9.31 ± 6.77 μg/m(3); P = .004). Multivariate analysis shows that for every 10 μg/m(3) increase of sulfur dioxide, there is an increase in the risk of hospitalization for ACS with SOL a 41% (odds ratio 1.41; 95% confidence interval 1.039-1.931; P = .028). CONCLUSIONS In our study population, exposure to high concentrations of sulfur dioxide is a precipitating factor for admission of patients with ACS and SOL.

Comprehensive Theoretical and Experimental Study of Short- and Long-Term Stability in a Passively Mode-Locked Solitonic Fiber Laser

We demonstrate the short- and long-term stable operation of an all-polarization-maintained Fabry-Pérot cavity passively mode-locked fiber laser. The laser operates in an all-anomalous-dispersion solitonic regime. Laser stability is studied by a variety of measurements, which confirm the high stability of the laser in the temporal and spectral-both optical and electrical-domains. Pulse durations of 540 fs, period-relative time jitters of ~0.0150/00, and long-term uninterrumped operation with 0.4% variation (standard deviation) in the average output power are obtained. The highly stable operation of the laser oscillator was maintained after amplifying the laser output with a conventional EDFA. Pulse durations of ~244 fs, period-relative time jitters of ~0.0190/00, and an average output power of 20 mW were obtained after amplification, while maintaining the 100-dB signal-to-noise ratio of the laser oscillator measured at 500-Hz offset from the fundamental harmonic frequency. The theoretical validation of our experimental results is based on solutions of the Nonlinear Schrödinger Equation. We demonstrate that wavelength and z -position dependences of the active medium gain must be taken into account for an accurate correspondence with the experimental properties of the laser.

Air pollution and heart failure: Relationship with the ejection fraction.

AIM To study whether the concentrations of particulate matter in ambient air are associated with hospital admission due to heart failure in patients with heart failure with preserved ejection fraction and reduced ejection fraction. METHODS We studied 353 consecutive patients admitted into a tertiary care hospital with a diagnosis of heart failure. Patients with ejection fraction of ≥ 45% were classified as having heart failure with preserved ejection fraction and those with an ejection fraction of < 45% were classified as having heart failure with reduced ejection fraction. We determined the average concentrations of different sizes of particulate matter (< 10, < 2.5, and < 1 μm) and the concentrations of gaseous pollutants (carbon monoxide, sulphur dioxide, nitrogen dioxide and ozone) from 1 d up to 7 d prior to admission. RESULTS The heart failure with preserved ejection fraction population was exposed to higher nitrogen dioxide concentrations compared to the heart failure with reduced ejection fraction population (12.95 ± 8.22 μg/m(3) vs 4.50 ± 2.34 μg/m(3), P < 0.0001). Multivariate analysis showed that nitrogen dioxide was a significant predictor of heart failure with preserved ejection fraction (odds ratio ranging from (1.403, 95%CI: 1.003-2.007, P = 0.04) to (1.669, 95%CI: 1.043-2.671, P = 0.03). CONCLUSION This study demonstrates that short-term nitrogen dioxide exposure is independently associated with admission in the heart failure with preserved ejection fraction population.

Short-and-long-term highly stable oscillation and amplification of linearly polarized passively mode-locked solitonic fiber laser resonators

In this work, we present a short- and long-term operation and environmentally-stable, all-polarization-mantained, Fabry-Pérot resonator, passively mode-locked fiber laser operating in an all-anomalous-dispersion solitonic regime. Our results confirm that the highly stable operation of the laser oscillator is maintained after amplifying the laser output with a conventional EDFA. Such stability has been studied by a variety of measurements in the temporal and spectral -both optical and electrical- domains before and after amplification. Pulse durations of 540 fs, period-relative time jitters of ~0.015‰, and long-term uninterrumped operation with <1.8% variation of the individually photodetected pulse peak powers are obtained for the laser oscillator. After amplification, dispersion-induced pulse durations of ~244 fs, period-relative time jitters of ~0.019‰ and an average output power of 20mW are obtained, while maintaining the 100 dB signal-to-noise ratio (SNR) measured at 500 Hz offset from the fundamental harmonic frequency of the photodetected signal. We have also carried out a theoretical validation of the emission properties of our laser oscillator based on solutions of the Nonlinear Schröedinger Equation that take into account wavelength and z-position dependence of the active medium gain.

All-fiber laser source for CARS-microscopy

Summary form only given. CARS microscopy is a highly desirable tool to provide real-time information e.g. in brain-cancer surgery [1] due to its label-free chemical imaging capabilities of living tissue. Still a widespread use in real-world applications has not been achieved due to the lack of suitable laser sources. Today widely used CARS laser sources based on Ti:Sapphire and parametric frequency conversion in bulk crystals are expensive and large while their operation requires technical staff devoted to alignment and maintenance. This restricts the application of CARS microscopy to specialized research laboratories only.In this contribution an all-fiber, hence alignment-free, CARS laser source and its application to CARS microscopy is presented. Key components in our setup are a passively mode-locked fiber oscillator delivering nearly transform-limited 50ps pulses at an optimized repetition rate of 2MHz, a fiber integrated amplification system and a fiber optical parametric frequency conversion stage using degenerate four-wave-mixing (FWM) in an endlessly single-mode fiber [2]. In addition we present a seeded FWM CARS source with an extremely high spectral resolution. The cw seed enhances the resolution more than one order of magnitude and allows for distinguishing between CH2 and CH3 resonances. Due to the long pulse durations of the generated signal and pump pulses the temporal walk-off is negligible which makes them ideal for fiber delivery, e.g. to the microscope, without complex delay lines. This enhances the simplicity greatly and makes this source particularly easy to use. 2. Experiment and results The mode-locked 50ps all-fiber oscillator was optimized to run at 2 MHz to avoid photo damage and provide enough peak power for the CARS process (fig.1a). An Yb-doped single-clad fiber amplifier boosts the average power up to 0.5W. The active fiber is spliced to the conversion fiber with a transmission of 74%. A conversion to 798nm, corresponding to a frequency separation of 2845cm-1 was realized. All components are fusion spliced and polarization maintaining to obtain alignment-free and robust operation.Ultrahigh spectral resolution of 1cm-1 was realized by a seeded FWM scheme (Fig. 1b). A laser scanning microscope was used to scan at Raman shifts of 2850cm-1 and 2930cm-1 mapping lipid and protein in a human aorta sample with artheriosclerotic plaque deposition (Fig. 1c). In conclusion, a novel approach for an all-fiber mono-laser source for CARS microscopy is presented. The frequency conversion is optimized to access a frequency shift of around 2850cm-1. Cw-seeding enhances the resolution greatly. Inherently synchronized pump and Stokes pulses are available at one fiber end, readily overlapped in space and time. The source is applied to CARS spectroscopy and microscopy experiments in the CH-stretching band. Due to its simplicity and maintenance-free operation, the laser scheme holds great potential for bio-medical applications outside laser laboratories.

Chromatic Dispersion Control in Mode-Locked Yb-Doped Fiber Lasers Based on a Microstructured Optical Fiber

We present an experimental study on the use of solid core microstructured optical fibers (MOF) for managing the chromatic dispersion in an Yb-doped fiber laser passively mode-locked by a saturable absorber. The performance of the laser, in terms of pulse width and repetition rate, was investigated as a function of the net cavity dispersion.

Tailoring the dispersion of photonic crystal fibers for supercontinuum and photon pairs generation

The interplay between chromatic dispersion and nonlinear effects is patent. Once a photonic crystal fiber (PCF) preform has been prepared, changing the parameters that control the fabrication process it is possible to adjust the dispersion properties of the fiber. In addition, it is very useful to develop postprocessing techniques that enable a fine adjustment of the dispersion along a section of PCF. The tapering of PCF, using a fusion and pulling technique, has been established as a rather useful technique to engineer the dispersion properties along tens of centimeters. Some of our recent experiments demonstrate that the use of erbium doped PCF enables an optical control of the dispersion through optical pumping of the rare earth ions. Our interest is focused on the exploitation of nonlinear PCF for the development of fiber light sources. Thus, we will present several experiments on supercontinuum and photon pairs generation, through degenerated four-wave mixing (FWM), in order to illustrate the control that one can achieve on the optical spectra of these light sources as a function of different dispersion control approaches.