Gian Luca Lippi

Deterministic chaos in laser with injected signal

Abstract Dynamic behaviour of an homogeneously broadened laser with injected signal is analyzed for a model in which the polarization is adiabatically eliminated. Detuning between the atomic resonant frequency, the cavity resonance and the frequency of the external signal is considered. We show that a transition to chaos via intermittency is possible for parameters appropriate for CO2 lasers.

Critical slowing down at a bifurcation

Critical slowing down near a bifurcation or limit point leads to a dynamical hysteresis that cannot be avoided by sweeping a control parameter slowly through the critical point. This paper analytically illustrates, with the help of a simple model, the bifurcation shift. We describe an inexpensive experiment using a semiconductor laser where this phenomenon occurs near the threshold of a semiconductor laser.

Differences in polarization dynamics of the electromagnetic field in xenon and neon lasers

Abstract We have experimentally observed the appearance of oscillations in the state of polarization of a constant-total-intensity, quasi-isotropic, HeXe, single-“geometrical”-mode laser operating at λ = 3.51 μm. Similar oscillations, accompanied by oscillations in the total intensity, have been detected also in a HeNe laser operating at λ = 3.3922 μm under the same experimental conditions. While the oscillations in the HeXe laser are understandable in terms of competition between the field amplitudes of two modes of different polarization, those in the HeNe may involve the atomic dynamics as well.

Deterministic mode alternation, giant pulses and chaos in a bidirectional CO2 ring laser

Abstract A CO 2 ring laser with a single longitudinal mode propagating in each direction shows a variety of stable, periodic, and aperiodic phenomena depending on gas pressure, cavity detuning and relative excitation. Three distinct low frequency time scales for dynamical behavior are observed and are explained by numerical solutions of an appropriate model.

Phase and frequency jumps in a bidirectional ring laser

Abstract Phase and frequency jumps are found to be part of the dynamical alternation of the direction of oscillation in a model for detuned homogeneously-broadened bidirectional ring lasers operating on a single mode in each direction. The frequency of each mode when it is dominant is that of the steady state unidirectional solution for that mode, but during the switching process it is increased or decreased with respect to the cavity frequency while it is declining or growing in intensity respectively. We are able to show analytically and numerically that near the minimum intensity for a suppressed mode the frequency jumps, and the combined relative phase of the fields and the population inversion grating switches by ±π radians.

Fabry-Pérot and ring cavity configurations and transverse optical patterns

Abstract The properties of travelling- and standing-wave resonators and their influence on the modal composition and propagation of transverse patterns are analysed and a prescription for constructing a travelling-wave resonator ‘equivalent’ to a standing-wave resonator is given. It is shown that the presence of an intracavity nonlinear medium invalidates the equivalence between the two kinds of cavity, even when the interference between the counterpropagating waves can be neglected. Therefore great care has to be taken when comparing experimental and theoretical results obtained in different types of cavity, since in general their properties differ. Some implications concerning the appearance of phase singularities in the two kinds of resonator are discussed.

Pump–probe spectroscopy of the sodium D1 line and the question of recoil-induced gratings in hot vapors

Abstract We present experimental and numerical results concerning the absorption properties of sodium vapor at moderate densities strongly driven by a pump field in the presence of a very low-intensity probe field and develop a three-level model for saturated absorption to better describe the hyperfine structure of the D 1 line. We show that this model is sufficient to explain our experimental results, and therefore conclude that recoil-induced gratings, in this configuration, are expected at higher pump and probe intensities.

High-speed direct modulation of semiconductor lasers

Direct modulation of the injected current still represents an attractive and inexpensive technique for encoding information in the output of a semiconductor laser. The growing requirements in volume of information to be transmitted and their conflict with the progressive, and rapid, degradation of the signal at high speeds have made this simple technical solution less and less attractive. A brief analysis of the sources of the problem is offered. A viable and inexpensive way of improving DMs performance is discussed. High quality signals are predicted at data transmission speeds that exceed by over an order of magnitude those obtainable with DM.

Route to Chaos in a CO2 Laser with Injected Signal

It is well known that the equations for a single-mode laser can be reduced to the Lorenz equations[1] and a chaotic behavior should be seen. However, this type of chaos has never been observed because of the actual values of the parameters in physical systems. Hence, it is necessary to introduce an external modulation[2] or to have a multimode laser where the degrees of freedom are larger than three. In these systems, experimental results have been reported [3–4]. In this communication a transition to chaos by intermittency is numerically shown in a single-mode laser with an injected signal without any modulated parameter. We refer to a CO2 laser medium where the pressure broadening provides a homogeneous gain line. A CO2 laser system has a relaxation time (1/γ|| = 10−3s) much larger than the dipole decay time (l/γ┴ = 10−8s); hence, the single mode dynamics is described by the coupling between two degrees of freedom (rate equations). Introducing an external field whose frequency ωl is detuned with respect to the cavity resonance ω0 and the atomic transition frequency ωc, we have the three degrees of freedom necessary for the onset of chaos.

Spontaneous Oscillations In A Single Mode Co2 Laser In A Fabry-Perot Cavity

We show the existence of self-pulsing at two characteristic frequencies in a single mode CO2 laser for low pump rates. The dynamical behavior of the system as a function of the pump rate, cavity losses and detuning between atomic and cavity frequencies has been investigated. These results can be explained by a recently developed theoretical model which incorporates intensity dependent parameters.