J. Pujol

Lorenz-like dynamics in Doppler broadened coherently pumped lasers

Abstract We report the theoretical interpretation of Lorenz-like behavior recently observed for the first time in a laser by Weiss and Brock [Phys. Rev. Lett. 57 (1986) 2804]. By means of a three-level laser model it is shown that in an optically-pumped far-infrared laser, coherent pumping effects are partially smeared out by Doppler broadening and as a result Lorenz-like dynamics may show up in some physical observables such as laser intensity.

Phase dynamics in a Doppler broadened optically-pumped laser

Abstract The dynamic behavior of the phase of the generated field in a Doppler-broadened optically-pumped far-infrared laser is theoretically investigated for the first time. The phase undergoes sudden jumps of approximately π radians, which allow to establish the actual symmetry of the main attractor in the phase space, explaining the heteroclynic character of the chaotic behavior observed in experiments.

Models, predictions, and experimental measurements of far-infrared NH3-laser dynamics and comparisons with the Lorenz-Haken model

Dynamics of the intensity and optical field amplitude of a coherently pumped far-infrared NH3-laser are measured and characterized. The experimental findings in certain parameter ranges closely follow the dynamics of the Lorenz model and its generalization for laser systems. Similarities and some specific differences are found in geometrical or statistical characterizations of the attractors. The experimental results are also consistent with the results of a model of optically pumped three-level lasers which takes into account the presence of a multiplicity of velocity groups as well as three-level coherence effects. For a certain region in parameter space, this far more complex model with a much larger phase space produces results similar to the dynamics of the Lorenz model. The model also provides explanations of differences between the experimental results and results from the Lorenz model.

Type-III intermittency in a four-level coherently pumped laser.

We study a homogeneously broadened four-level model for a coherently pumped laser with pump and laser fields having crossed linear polarizations. For a parameter range of the type explored in the experiments by Tang et al. [Phys. Rev. A 44, R35 (1991)] the system exhibits a family of type-III-intermittency transitions to chaos in which the onset of intermittency is preceded by period-2, period-3, or period-4 states. We find similarities but also differences between the results of our theory and their experimental results

Instabilities in optically pumped infrared lasers

The unstable emission of an optically pumped FIR gas laser is theoretically analysed through numerical resolution of the associated Maxwell-Bloch equations. The instability domain in the main control parameters space is determined and an example of chaotic behaviour is examined.

Probe spectroscopy of three-level systems with a standing-wave saturator: Influence of the saturator detuning

Abstract The absorption of a weak laser beam probing a Doppler-broadened three-level system saturated by a standing-wave pump is studied theoretically for the case of small saturator detunings. The features of the obtained absorption spectra are analysed by means of the dressed-atom approach. A strong influence of radiative and high-order multi-photon processes is showed. The influence of saturator tuning fluctuations on the narrow Doppler-free peak which appears in the resonant case is analysed and its consequences for high-resolution applications are considered.

Standing-wave and intensity effects in intracavity laser RF double resonance spectroscopy

Abstract The laser and RF absorption spectra in a laser-RF double resonance configuration with the gas sample placed inside the laser cavity are exactly calculated by means of a semiclassical three-level model and interpreted through the dressed atom approach. Laser standing-wave effects and intensity effects are studied. Several kinds of nonlinear coherent phenomena are evidence. High-resolution spectroscopic applications are considered.

Dynamics of a detuned, optically pumped far-infrared laser

The dynamic behaviour of a coherently pumped single-mode far-infrared ring laser with a homogeneously broadened three-level medium is analysed theoretically, considering detuning between amplifying transition and cavity frequencies. Phase diagrams as a function of cavity detuning and amplitude of the resonant pump field have been obtained, which show different domains of stationary, oscillatory and chaotic output. In some conditions the laser is shown to exhibit hysteresis between different regular self-pulsing regimes, i.e. the phenomenon of generalised bistability.

Progress in Modelling Coherently Pumped Far-Infrared Laser Dynamics

Coherently pumped lasers (CPL) operating in the far-infrared spectral region shown a wealth of instabilities1, including a behavior remarkably similar2,3 with the predictions of the paradigmatic Lorenz-Haken model of a single-mode homogeneously broadened laser4,5. The qualitative agreement; between theory and experiments2,3 was rather surprising, for the model4,5 refers to a two-level system whereas the CPL operate on a three-level scheme, where the pumping and lasing transitions share a common upper level. Dupertuis et al.6 have identified conditions for the mathematical reduction of the CPL equations to the Lorenz-Haken equations4, but these conditions were not all fulfilled in the experiments of Weiss and collaborators2,3.