J. R. Rios Leite

Measurement of high‐order optical nonlinear susceptibilities in semiconductor‐doped glasses

The optical susceptibilities of CdSxSe1−x ‐doped glasses were observed up to χ(11) using a spatially resolved phase‐matched multiwave mixing technique. Using a pulsed dye laser tuned near the band gap, measurements were performed for ‖χ(3)‖, ‖χ(5)‖, and ‖χ(7)‖ in four different commercial filter glasses.

Control of Lorenz chaos

Abstract Controlling of chaos present in the Lorenz system is demonstrated numerically by coupling periodic modulations to the control parameter. The calculated bifurcation maps and the spectra of Lyapunov exponents show that the chaotic system will be stable over a large range of parameters of the periodic modulations. These results may be applied to other chaotic systems described by a set of differential equations.

Ultrafast chi /sup (3)/-related processes in semiconductor doped glasses

Experimental results are described for exploiting the fast and large nonlinear susceptibility of semiconductor-doped glasses (SDGs). Self-diffraction experiments were performed using incoherent broadband lasers with femtosecond time resolution yielding new information on the time response of the SDG nonlinearity. The use of backward nondegenerate wave-mixing to demonstrate yellow-to-green frequency conversion with femtosecond resolution is reported. In addition, results are presented which demonstrate the use of the SDG as a picosecond all optical gate at a 100-MHz repetition rate. >

Lineshape of cooperative two-photon absorption by atom pairs in solids

Abstract The simultaneous absorption of two photons by a pair of atoms embedded in a solid is theoretically studied. A cooperative resonance is analysed as a new possibility for probing pair interaction in doped crystals.

Time delays in the synchronization of chaotic coupled lasers with feedback

Isochrony and time leadership was studied in the synchronized excitable behavior of coupled chaotic diode lasers. Each unit of the system had chaos due to feedback with a fixed delay time. The inter-units coupling signal had a second, independent, characteristic time. Synchronized excitable spikes present isochronous, time leading or time lagging behavior whose stability is shown to depend on a simple relation between the feedback and the coupling times. Experiments on the synchronized low frequency fluctuations of two optically coupled semiconductor lasers and numerical calculations with coupled laser equations verify the predicted stability conditions for synchronization. Synchronism with intermittent time leadership exchange was also observed and characterized.

Degenerate multiwave mixing in SF6

Abstract High-order diffraction of CW CO 2 laser radiation was observed in SF 6 in the Doppler broadening limit. The nonlinear susceptibilities, up to χ (9) , were separately monitored in Doppler free resonance lineshapes, using a near-collinear phase matched multiwave mixing configuration.

Methyl alcohol saturation spectroscopy using a CO 2 sequence band laser

Doppler-free saturated absorption spectra of CH(3)OH at 300 and 600 K have been observed with a cw CO(2) sequence-band laser tunable over 60 lines in the 9.4- and 10.6-microm bands. Sixteen inverted Lamb dips were observed.

Coupling of two chaotic lasers

Abstract Numerical solutions for two sets of equations describing lasers with intracavity saturable absorbers were studied for their instabilities associated to passive Q -switching. For realistic values of parameters of CO 2 lasers, we have demonstrated that two independent chaotic lasers can to into synchronized periodic oscillation after 3% of coupling. If both lasers start from periodic oscillation, after coupling they can go into either synchronized periodic or synchronized chaotic oscillations depending on the coupling strength. The coupling can be made either through absorber, laser gain or both.

Infrared to visible image frequency conversion in Cd(S,Se) glass composites

Wave mixing experiments are reported using two infrared and one visible laser beams which are incident on a semiconductor doped glass. The mixing process produces infrared to visible image conversion via the material electronic nonlinearity with fast (less than 20 ps) time response.

Experimental bifurcations and homoclinic chaos in a laser with a saturable absorber

The shape and the peak values of the pulses from a passive Q-switching CO2 laser with SF6 as saturable absorber were detected while the laser was tuned in frequency across a longitudinal mode. A succession of stability windows, typical for bifurcation diagrams in the homoclinic scenario, was observed and the widths of those windows were measured. The expansion rate of the undulations in individual pulses was also obtained and compared to Floquets multipliers given by the ratio of widths in consecutive windows. The dynamics is consistent with a homoclinic tangency to a periodic orbit.