Experimental Nonlinear Dynamics of Laser Systems

We propose an experimental study of controlled regimes in an Nd-doped yttrium aluminium garnet (Nd:Ya1G) laser and in small ensembles of coupled CO2 lasers (2-4) modules coupled according to different schemes). Nd:YA1G lasers are believed to display an intrinsic chaotic behavior-1 at sufficiently high pumping power. Long experimental time series from such a system will be re-examined and the reliability of the numerical estimation of the Lyapunov spectra checked against recently proposed criteria2. Some other criteria of distinguishing chaos from an "amplified noise"-3 will be used. An attempt will be made to obtain the chaotic regime of lasing for this laser by different means such as periodic modulation of some system parameters, radiation injection from another lasing unit and different feedback schemes -4. Being sure that the system indeed resides on a low-dimensional attractor for some of the tested regimes, we intend to reexamine the technique of stabilization of unstable periodic orbits embedded in an attractor by the occasional proportional feedback method-5 already demonstrated effective for the Nd:YA1G laser-1 in the autonomous chaotic regime. The experience from this series of experiments will be used in an attempt of controlling intrinsic and/or induced chaos in small arrays of up to four coupled CO-2 lasers. Different coupling schemes and array geometries will be used. There is a theoretical and restricted experimental evidence that at least some coupling schemes (e.g., two CO2 lasers optically coupled by a semitransparent mirror-6) are indeed chaotic and can be described by low dimensional systems of ODE's. The same as above methods of testing chaos will be used and the stabilization of the periodic orbits attempted for some of the realizations of coupled arrays.