F. de Tomasi

Instabilities and chaos in an infrared laser with saturable absorber: experiments and vibrorotational model

The instabilities and chaos in a CO2 laser containing SF6 and 15NH3 absorbers have been studied as a function of the parameters. By making use of a phase-portrait analysis, the instabilities have been classified through laser-control orbits in the phase space around the laser-with-saturable-absorber (LSA) fixed points. A chaotic regime, their a sequence of period-doubling bifurcations, has been observed for an instability of limit cycles reached through one fixed point. The transition between different instability operations presents an intermediate regime, around defined as the hesitation regime and have characterized through the fluctuations in the return times. which we have phenomena have been reproduced within a model, including the rotational–vibrational structure of The observed and absorber media. The numerical analysis has shown that the LSA time evolution, as described the amplifier orbits in the LSA phase space, depends on the relative attractions of the saddle point and the through homoclinic saddle focus fixed points.

Experimental study of caesium energy pooling collisions and modelling of the excited atom density in the presence of optical pumping and radiation trapping

An experimental study of caesium energy pooling collisions, , at thermal energies, has been carried out in a capillary cell using diode laser excitation. Use of the capillary cell minimizes the effects of radiation trapping, but nonetheless, such effects still play a significant role in the analysis. Consequently, a rate equation model, which treats simultaneous effects of saturation, optical pumping, and radiation trapping, has been developed and is used to determine the atom density under these experimental conditions. The excited atom densities are combined with measured fluorescence ratios to determine rate coefficients for the caesium energy pooling process. Our values for these rate coefficients are in agreement, within combined error bars, with values we have recently obtained under very different experimental conditions.

Lineshape changes in an optically thick Na vapour with a buffer gas

Abstract In a dense Na vapor, we have investigated the changes in the Doppler-broadened shape of the D 2 line produced by the combined effect of laser induced hyperfine optical pumping and collisions. The observed narrowing of the excitation spectrum observed on the backward scattered fluorescence light is explained by a simple rate equation model.

Influence of noise on the quasi-homoclinic behavior of a laser with saturable absorber

Abstract The influence of noise on a laser with saturable absorber is investigated. In particular, the effect of an external added noise on the return time fluctuations and on the hesitation regime is studied. Numerical simulations based on a model with three-levels in the amplifier and four-levels in the absorber lead to an interpretation of of these behaviors.

Collision induced fluorescence in Cs vapor excited by a laser diode

Two experiments on cesium vapor at relative low number densities (≊1010÷1013 cm−3), excited at the first resonance transition 6S1/2→6P3/2 (λ=852 nm) by a cw laser diode are reported. We have measured the rate coefficients at thermal energies for the energy pooling to the 7P levels. In presence of Ne as buffer gas we have observed a striking distortion of the line‐shape.

Evolution of the beam quality factor for various active medium positions within a Gaussian cavity

Abstract A 2-m-long plane-parallel cavity with a Gaussian reflectivity mirror has been applied to a XeCl discharge chamber with a 35-cm-long active medium and the temporal evolution of the main parameters of the intracavity laser radiation after reflection on the Gaussian mirror, has been analysed for various active medium positions within the cavity. It is shown that in cavities of equal length and effective Fresnel number, the properties of the intracavity radiation are dependent on the Gaussian mirror distance from the active medium, since the onset of laser action. Indeed, it has been found that the beam quality factor M 2 reaches smaller values by setting the Gaussian mirror closer to the active medium. It is also shown that a theory formerly developed for the evolution of the parameters of Schell–Gauss model beams propagating in Gaussian-mirror cavities provides a satisfactory description of experimental results.