Alejandro A. Hnilo

Extreme events in the Ti:sapphire laser.

We report experimental and theoretical evidence of the existence of extreme value events in the form of scarce and randomly emerging giant pulses in the femtosecond (self-pulsing or Kerr-lens mode-locked) Ti:sapphire laser. This laser displays complex dynamical behavior, including deterministic chaos, in two different regimes. The extreme value pulses are observed in the chaotic state of only one of these two regimes. The observations agree with the predictions of a well-tested theoretical model that does not include noise or self-Q-switching into its framework. This implies that, in this laser, the extreme effects have a nontrivial dynamical origin. The Ti:sapphire laser is hence revealed as a new and convenient system for the study of these effects.

Self-mode-locking Ti:sapphire laser description with an iterative map

Analytical expressions for the pulse variables (duration, energy, chirp, beam size, and curvature) of a self-mode-locked laser are obtained in the form of a five-dimensional iterative map from the full time-and-space (4 × 4) matrix formalism and the gain-equal-to-loss condition. In spite of the great simplifications involved, the model shows good agreement with other authors’ reported experimental data and detailed numerical simulations. The aim is that map theory be used to yield insight into the dynamics of self-mode-locked lasers. As an example of a practical application regions of dynamically stable laser operation in the parameter space are computed.

Extreme events and crises observed in an all-solid-state laser with modulation of losses.

We report observations of extreme events (or dissipative optical rogue waves) in a laser with a modulated parameter (cavity losses). Experimental data supporting the hypothesis that these events are related with multi-stability and external crises is presented. It is also shown that the time separation between a pulse and an extreme event can be predicted more accurately than that between pulses of average intensity, in agreement with the theoretical description and opening the road to the prediction and control of extreme optical events.

Measuring the entanglement of photons produced by a nanosecond pulsed source

A source of entangled photons based on well-separated laser pump pulses (PDs) with a duration in the nanosecond range may be useful in many applications. Yet, such a source has intrinsic problems arising from the simultaneous arrival of signal and noise photons to the detectors, which makes the methods unsuitable for dealing with accidental (or spurious) coincidences applied in the continuous-wave or mode-locked pump regimes. Those problems are analyzed, and practical methods to calculate the number of accidental coincidences are described and experimentally checked. These methods are useful not only to measure entanglement, but also in every situation where extracting the number of valid two-photon coincidences from noisy data generated by such a pulsed process is required. As an original example of the use of these methods, we present the time-resolved measurement of the concurrence of the field produced by spontaneous parametric downconversion with PDs of duration in the ns range at a repetition of kHz.

Transverse diode-pumped neodymium-doped yttrium vanadate laser of simple design

Abstract. The design and performance of an all-solid-state Nd:YVO 4 laser, transversely pumped by a single 20-W at 808 nm diode with nocoupling optics, are presented. The prototype, which is devised to be thesource of a micro-LIDAR station, is very simple, easy to align, compact,and stable. The key element is a roof prism as the end mirror of the lasercavity, which is used to symmetrize the effects of the thermal distortionand the inhomogeneity of the population inversion distribution. Typicalnumbers are 4.2-W cw with a slightly astigmatic 3:2 homogeneous spotand a divergence of 0.5 mrad. The protoype is also tested in the activeQ-switching mode, providing pulses 50-ns full width at half maximum FWHM at 14 KHz, 3.5 W average. Frequency doubling external to thecavity in a nonoptimized configuration provides 700 mW at 532 nm.