José R. Rios Leite

Quantum mechanical features of optically pumped CW FIR lasers

Quantum mechanical predictions for the gain of an optically pumped CW FIR laser are presented for cases in which one or both of the pump and FIR transitions are pressure or Doppler broadened. The results are compared to those based on the rate equation model. Some of the quantum mechanical predictions are verified in CH 3 OH.

Effective masses and complex dielectric function of cubic HfO2

The electronic band structure of cubic HfO2 is calculated using an ab initio all-electron self-consistent linear augmented plane-wave method, within the framework of the local-density approximation and taking into account full-relativistic contributions. From the band structure, the carrier effective masses and the complex dielectric function are obtained. The Γ-isotropic heavy and light electron effective masses are shown to be several times heavier than the electron tunneling effective mass measured recently. The imaginary part of the complex dielectric function ϵ2(ω) is in good agreement with experimental data from ultraviolet spectroscopic ellipsometry measurements in bulk yttria-stabilized HfO2 as well as with those performed in films deposited with the tetrakis diethylamido hafnium precursor for energies smaller than 9.5eV.The electronic band structure of cubic HfO2 is calculated using an ab initio all-electron self-consistent linear augmented plane-wave method, within the framework of the local-density approximation and taking into account full-relativistic contributions. From the band structure, the carrier effective masses and the complex dielectric function are obtained. The Γ-isotropic heavy and light electron effective masses are shown to be several times heavier than the electron tunneling effective mass measured recently. The imaginary part of the complex dielectric function ϵ2(ω) is in good agreement with experimental data from ultraviolet spectroscopic ellipsometry measurements in bulk yttria-stabilized HfO2 as well as with those performed in films deposited with the tetrakis diethylamido hafnium precursor for energies smaller than 9.5eV.

Detecting photons in the dark region of Laguerre-Gauss beams.

We show that a photon detector, sensitive to the magnetic field or to the gradient of electric field, can help to characterize the quantum properties of spatially-dependent optical fields. We discuss the excitation of an atom through magnetic dipole or electric quadrupole transitions with the photons of a Bessel beam or a Laguerre-Gauss (LG) beams. These spiral beams are shown to be not true hollow beams, due to the presence of magnetic fields and gradients of electric fields on beam axis. This approach paves the way to an analysis at the quantum level of the propagating light beams having a complicated spatial structure.

Power law periodicity in the tangent bifurcations of the logistic map

Numerical studies were carried out for the average of the logistic map on the tangent bifurcations from chaos into periodic windows. A critical exponent of 12 is found on the average amplitude as one approaches the transition. Additionally, the averages oscillate with a period that decreases with the same exponent. This Power Law Periodicity is related to the reinjection mechanism of the map. The undulations appear at control parameter values much earlier than the values where the critical exponent of the bifurcation shows significant changes in the average amplitude.

Analog circuits simulation of communication with chaotic lasers

Masked signal communication between two chaotic lasers, described by rate equations, was implemented using analog circuits. Digital modulation of the gain parameter in the master circuit generated the messages. It is shown that there is a level of modulation for which the receiver circuit decodes the signal by on-off synchronization while the Poincare sections, the first return maps and the time of return maps recovered directly from the master signal could not distinguish the bits. The circuits simulate the dynamics of two optically coupled CO2 lasers with intracavity saturable absorber. The signal appears to be unbreakable in such low dimensional systems because they operate at homoclinic chaos which corresponds to multibranched one-dimensional return maps.

Angular dependence of phase conjugation in SF 6

Optical phase conjugation by degenerate four-wave mixing in SF(6) was studied with a cw CO(2) laser. The intensity and angular dependence of reflectivity were measured for the 10.6-microm P(18) line. The results verify the predictions of the inhomogeneously broadened resonant two-level gas model.

Shannon capacity and codes for communicating with a chaotic laser

We investigate a method of communicating with chaos described by Hayes, Grebogi, and Ott (19913), which uses the idea of controlling chaos by small perturbations. Although allowing the electronics controlling the output signal to remain at the low-power level, this method unavoidably incurs a capacity loss, which we calculate for a chaotic CO/sub 2/ laser model. We first determine an approximation to the laser language, by means of a forbidden set representation, and then find its Shannon (1963) capacity. The results indicate that, since the capacity loss is not significant, the tradeoff is worthwhile. Finally, we point to simple finite-state encoders that satisfy the constraints imposed by the language.

Bifurcations and averages in the homoclinic chaos of a laser with a saturable absorber

The dynamical bifurcations of a laser with a saturable absorber were calculated, with the 3–2 level model, as a function of the gain parameter. The average power of the laser is shown to have specific behavior at bifurcations. The succession of periodic–chaotic windows, known to occur in the homoclinic chaos, was studied numerically. A critical exponent of 12 is found at the tangent bifurcations from chaotic into periodic pulsations.

Deterministic chaos in an ytterbium-doped mode-locked fiber laser

We experimentally study the nonlinear dynamics of a femtosecond ytterbium doped mode-locked fiber laser. With the laser operating in the pulsed regime a route to chaos is presented, starting from stable mode-locking, period two, period four, chaos and period three regimes. Return maps and bifurcation diagrams were extracted from time series for each regime. The analysis of the time series with the laser operating in the quasi mode-locked regime presents deterministic chaos described by an unidimensional Rössler map. A positive Lyapunov exponent λ = 0.14 confirms the deterministic chaos of the system. We suggest an explanation about the observed map by relating gain saturation and intra-cavity loss.

Simuation of Masked Communication with Chaotic Lasers DOI: 10.14209/jcis.1997.14

This paper describes communication with chaotic laser pulses. An information bearing signal is masked within the chaotic carrier pulses and recovered via chaos synchronization in a chaotic receiver. Two analog circuits, representing chaotic CO2 lasers, simulate the system. The chaotic pulsation from the first circuit was modulated and transmitted to the second one which behaved like a receptor, demodulating the chaotic signal through synchronism. Temporal series give power spectrum and return maps from Poincare section of transmitted signal. In these no trace of modulation is observable, which verifies the masked nature of the sent messages.