Marcelo G. Kovalsky

Stability and bifurcations in Kerr-lens mode-locked Ti:sapphire lasers

Abstract Kerr-lens or self-mode-locked Ti:sapphire lasers are known to display several modes of operation, depending on the values taken by the system’s parameters. The basic observed modes of operation are: continuous wave, mode locking with transform limited pulses, and mode locking with chirped pulses. These modes are naturally obtained from a description based on an iterative or Poincare map of five pulse variables (beam size curvature, pulse duration, chirp and energy). The stability of these modes is obtained for an experimentally accessible range of the parameters. The theoretical predictions agree qualitatively with the experimental observations. For a particular bifurcation, we study the feasibility of an approximate description of the (five variables) dynamics with a one-variable map, which results in the logistic map.

Hidden instabilities in the Ti:sapphire Kerr lens mode-locked laser

It is experimentally shown that pulse-to-pulse instabilities in the output of Kerr lens mode-locked Ti:sapphire lasers are usual and that they can affect some of the pulse variables (e.g., the spot size) and not others (e.g., pulse duration and energy). These instabilities are not detectable in the averaged signals (such as the autocorrelation of the pulse) that are customarily used for controlling the laser. But, if they are present but are disregarded, these instabilities have undesirable consequences in almost any application. A simple way to detect and eliminate the instabilities is described.

Optical rogue waves in an all-solid-state laser with a saturable absorber: importance of the spatial effects

We study the features of the optical rogue waves (ORWs) observed in an all-solid-state (Cr:YAG+Nd:YVO4) passively-Q-switched laser, which is a system of wide practical interest. The extreme events appear as isolated pulses of extraordinary intensity during the chaotic regime of this laser. The standard theoretical description (three-level rate equations for a single mode of the field and a two-level system for the absorber) does predict the existence of many of the observed dynamical features, including chaos, but it fails to predict the existence of ORWs. Faced with the problem of improving the theoretical description, we find that ORWs are observed only when the Fresnel number of the laser cavity and the embedding dimension of the attractor reconstructed from the experimental time series are high, and the laser spot profile has a spatially complex structure. These results suggest that spatial effects are an essential ingredient in the formation of ORWs in this type of laser.

Bistability in Kerr lens mode-locked Ti:sapphire lasers

Femtosecond pulse Ti:sapphire lasers can operate in different ways for the same values of the control parameters. This phenomenon of multistability is explained in a simple way by a theoretical approach using iterative or Poincare maps. We present experimental confirmation of the predictions of the approach regarding the slope (of pulse duration vs. group velocity dispersion) and regions of stability of two different regimes of mode locking, i.e. transform-limited and chirped output pulses.

Features of the extreme events observed in the all-solid state laser with a saturable absorber

Extreme events in the form of pulses of extraordinary intensity (sometimes also called optical rogue waves) are easily observed in the chaotic regime of an all-solid-state laser with a saturable absorber if the Fresnel number of the cavity is high. This result suggests that the nonlinear interaction among transverse modes is an essential ingredient in the formation of extreme events in this type of laser, but there is no theoretical description of the phenomenon yet. We report here a set of experimental results on the regularities of these extreme events in order to provide a basis for the development of such a description. Among these results, we point out here (i) the decay of the correlation across the transversal section of the laser beam, and (ii) the appearance of extreme events even if the time elapsed since the previous pulse is relatively short (in terms of the average interpulse time interval), which indicates the existence of some unknown mechanism of energy storage. We hypothesize that this mechanism is related to the imperfect depletion of the gain by some of the transversal modes. We also present evidence in support of this hypothesis.

Extreme value events in self pulsing lasers

We report experimental and theoretical evidence of the existence of extreme value events (sometimes named “optical rogue waves”) in two types of lasers of widespread use, both belonging to the “laser with a saturable absorber” scenario. One is the Kerr-lens-mode-locking Ti:Sapphire (fs pulses) laser, the other one is the all-solid-state Cr+Nd:YAG (ns pulses) laser. Extreme value events are observed in some (not all) the chaotic regimes of both lasers. A well-tested theoretical model, based on a five variables iterative map, describes the observations for the former case in a complete way. The usual description in terms of rate equations apparently fails to predict extreme events for the latter, implying that this description must be improved.

Bistable Behavior of a Kerr Lens Mode Locked TI: sapphire Laser.

Kerr lens mode locked Ti:Sapphire lasers can operate in at least two pulsed modes. Several models were developed with the aim to describe the characteristics of these modes. Those based on iterative maps, can reproduce the structurally stable properties of each mode but are unable to describe the interaction between modes. In this paper, we present a numerical simulation based on a complete map equation that makes possible to accurately describe the bistability experimentally observed in the laser. With the numerical time series we determine that the bistable behavior corresponds to low dimensional deterministic chaos and calculate that the embedding dimension of the attractor is three.

Optical rogue waves in the solid-state laser with a saturable absorber

We study the features of the optical rogue waves (ORW) observed in an all-solid-state (diode-pumped, Cr:YAG+Nd:YVO4) passively-Q-switched laser, which is a system of wide practical interest. The extreme events appear during the chaotic and hyper-chaotic regimes of this laser, in one of two forms: 1) as isolated pulses of large intensity (“Intensity ORW”) or: 2) as a long time between pulses (“Time ORW”). These two types of extreme events are not correlated (i.e., an I-ORW is not always preceded or followed by a T-ORW). The standard theoretical description of this laser system (three-level rate equations for a single mode of the field and a two-level system for the absorber) is not able to predict these phenomena, not even the mere existence of ORW. Faced with the problem of improving the theoretical description, we find that ORW are observed if the Fresnel number of the laser cavity and the embedding dimension of the attractor reconstructed from the experimental time series are high, and the laser spot profile presents a spatially complex structure. These results suggest that the spatial effects are an essential ingredient in the formation of ORW in this type of lasers.

Measuring polarization entanglement with a pulsed source

Bells inequality is measured recording the time of arrival of the pulses and detection of each single photon. The obtained results impose new restrictions to the class of hidden-variables theories that exploit the