Salvador Balle

Pulse shielding in Laser-Induced Breakdown of saline water on hydrodynamic time scales is experimentally characterized. Pairs of pulses from a Nd:YAG laser are focused into saline water with a controlled time delay between them. The Laser-Induced Breakdown produced by the first pulse creates a cavitation bubble that later collapses generating a plume of bubbles that evolves on hydrodynamic time scales. When the second pulse arrives, the light is scattered by this plume with a consequent reduction in the intensity at the focal spot resulting in a lower breakdown efficiency of this pulse. By means of acoustic measurements, we determine the breakdown energy threshold for the first pulse and characterize the shielding of the second pulse as a function of the salinity of the solution, the energy of the pulse, and the inter-pulse interval. A model for the blocking process that takes into account both linear and nonlinear absorption along the path is developed which satisfactorily explains the observations.

We study theoretically and experimentally the combined effects of polarization-selective optical feedback and of crossed-polarization reinjection in a vertical-cavity surface-emitting laser. We show that the application of polarization-selective optical feedback, which induces an effective dichroism in the system, allows one to generate a robust and regular square-wave output signal in each polarization component. The period of the square-wave signal is determined by twice the reinjection delay. We analyze the regularity of the induced modulation as a function of laser bias current, dichroism, and of the levels and delays of reinjection and feedback, thus revealing the robustness of the square-wave emission in the parameter space. We also show that the feedback is more effective when acting on the long-wavelength polarization mode, which can be traced to the asymmetry of the bistable region of the vertical-cavity surface-emitting lasers for low dichroism.

Multimode dynamics in bidirectional laser cavities can be accurately described by folding space into time delay. This results in a set of delayed algebraic equations that preserve the dynamics of all cavity modes while drastically reducing number of degrees of freedom. This reduction allows for both linear stability analysis and bifurcation diagram reconstruction, as well as integration times reduced by orders of magnitude.

Passively mode-locked semiconductor lasers, and the modelling strategies developed on the basis of Travelling-Wave Models are reviewed.

The performance of two-section, passively mode-locked semiconductor lasers is theoretically analyzed for different cavity designs. Placing the saturable absorber section close to an antireflection-coated facet leads to a substantial increase in output power and a reduction in amplitude and timing jitter. Moreover, it broadens the bias current region of stable passive mode-locking operation.

In this paper, we present an experimental and theoretical study of passive mode-locking in semiconductor Fabry-Pérot, quantum-well, lasers operating at around 1550 nm and producing picosecond pulses at a repetition frequency of 40 GHz. The different regimes that occur as the reverse bias voltage applied to the saturable absorber (SA) section or the bias current injected into the amplifier section are characterized both in the time and frequency/wavelength domains. Our results reveal that the lasers display spectral competition between the gain of the amplifier section and the absorption of the SA, with variations of the lasing wavelength up to 25 nm as the bias conditions are changed. These wavelength variations result from the thermal drift of the SA band-edge due to Joule heating by the generated photocurrent and from the competition between two possible lasing regions placed either at the amplifier gain peak or near the band-edge of the SA. The experimental observations are satisfactorily reproduced and explained in the framework of a Traveling Wave Model complemented by a time-domain description of the semiconductor susceptibility.

We studied the influence of the topography on the oceanic response to a traveling atmospheric disturbance and the relevance of its propagation direction on the generation of seiche oscillations. A primitive equation ocean model was used to analyze the response of two harbors located in insular systems to a pressure disturbance. The spectral component at the frequency of fundamental harbor resonance was determined from these data for different propagation directions of the incoming atmospheric disturbance. A conceptual model of interferences of resonantly generated ocean waves was introduced in order to explain energy maxima obtained by the numerical model close to the most affected areas.

All-optical directional switching of bistable semiconductor ring lasers is studied by numerical simulations of a traveling-wave model. We discuss how the reversal depends on the bias current applied to the laser as well as on the energy, duration, and wavelength of the trigger pulses. For pulse durations longer than the cavity roundtrip time, the reversal occurs smoothly with a transient that exhibits relaxation oscillations, otherwise, the transient is composed of large long-lived spikes that reveal its multimode character. In the former case, the switching speed can be defined like in electronics systems, but not in the latter, which requires an operational definition of the maximum speed based on, e.g., bit-error rate measurements. Our model includes the light extraction sections present in real devices, which allows us to discuss the experimental problems posed by the differences existing between intracavity fields and output fields.

Contrary to common belief, empirical evidence shows that a number of marine littoral fish species tend to remain in a small geographic area. Despite the growing awareness about the consequences of reduced mobility (e.g. design of marine protected areas), an accurate description of fish movement is technically difficult; thus, it is usually not considered. Mark-release-(single)-recapture (MRsR) data obtained from externally tagged fish that are returned by fishermen or recreational fishers are potentially useful for describing fish movement. The present study is a methodological contribution aimed at demonstrating a simple analytic strategy for estimating the size of the circular home range (i.e. the area where a fish spends most of the time) from MRsR data. This analytic strategy is not adequate for pelagic or large predators moving at the oceanic scale but could be suitable for some reef or littoral fish. The estimates obtained by this method are robust even if (1) the number of recaptured fish is small, (2) fishing effort or habitat suitability displays some spatial variability and (3) fish display some intra-specific variability. Based on only 32 recaptures, our data demonstrate that Coris julis (a small labrid targeted by recreational fishers) is more sedentary than previously assumed; this fish spends 95% of its time within an area 227 m in radius (Bayesian 95% credibility interval: 192 to 275 m). © Inter-Research 2011.The present study was financed by the ROQUER (CTM2005-00283) and CONFLICT (CGL2008-958) projects and funded by the Spanish Ministry of Research and Science; the ACOUSTIC TRACKING (UGIZC) research project was funded by the Govern de les Illes Balears. D.M. and J.A. had a fellowship supported by the Spanish Ministry of Research and Science.Peer Reviewe