No abstract available

[en] Many physical problems, especially light-propagation, that involve the Laplacian operator, are naturally connected with Fourier or Hankel transforms (in case of axial symmetry), which both remove the Laplacian term in the transformed space. Sometimes the analytical calculation can be handled at its end, giving a series or an integral representation of the solution. Otherwise, an analytical pre-treatment of the original equation may be done, leading to numerical computation techniques as opposed to self-adaptive stretching and rezoning techniques, which do not use Fourier or Hankel transforms. The authors present here some basic mathematical properties of infinite and finite Hankel transform, their connection with physics and their adaptation to numerical calculation. The finite Hankel transform is well-suited to numerical computation, because it deals with a finite interval, and the precision of the calculation can be easily controlled by the number of zeros of J₀(x) to be taken. Moreover, they use a special quadrature formula which is well connected to integral conservation laws. The inconvenience of having to sum a series is reduced by the use of vectorized computers, and in the future will be still more reduced with parallel processors. A finite-Hankel code has been performed on CRAY-XMP in order to solve the propagation of a CW optical beam in a saturable absorber. For large diffractions or when a very small radial grid is required for the description of the optical field, this FHT algorithm has been found to perform better than a direct finite-difference code

[en] Laser temporal-coherence effects are investigated in four-photon ionization of cesium atoms when the Nd-glass laser frequency is tuned to the resonant three-photon transition 6S → 6F. It is shown experimentally for the first time that resonance shift with incoherent laser pulses is enhanced by a factor 2.8 +- 0.2 compared to the shift with coherent pulses. (orig.)

[en] A comprehensive effort is being carried out to study the phenomena associated with the co-propagation of two different-wavelength optical pulses in a nonlinear homogeneously broadened three-level atomic system which can sustain amplification or absorption. This is a double self-induced-transparency. The atomic configuration can be cascade, lambda or vee. The beams strongly influence each other by exchanging energy back and forth with the resonant medium. The semi-classical formalism is adopted as well as the slowly-varying-envelope approximation. The principal motivation is reaching an understanding of this fundamental double resonance interaction and elucidating the temporal synchronization and the single-photon distortion free co-propagation for each beam in Double Self-Induced-Transparency SIT, Two-color super-fluorescence and coherent pump depletion effects on (a) Stokes and (b) Super-fluorescence buildup. Extension of this current research to multi-level systems would be relevant to laser chemistry and laser isotope separation

[en] The saturable absorption, which varies from one concentric shell to another, (namely, the loss decreases with increasing intensity and attenuates the low-intensity 'wings' of the beam more than the high-intensity 'center', thus narrowing a beam propagating through), strips the beam edges which forms a shrinkage aperture. The inward intensity flow does not experience a nonlinear boosting amplification as in the unexpected but numerically predicted self-focusing in SIT since there is not any population inversion in shells closer to the axis. This fact must have been recognized by other investigators when they developed their model in which an aperture stop approximates the stripping of the beam encoding by the non-uniform absorption and then allowed for free space propagation. The stripping and the early stages of an inward flow of intensity can be described perturbatively, but such treatments only describe the onset of the enhancement; the perturbation must be followed by a free space propagation so that the same on-axis self-focusing, obtained by rigorous calculations, occurs. The propagation in free space of a parabolic beam is expressed analytically as an equivalence to the aperture model where absorption induced stripping is followed by a pure diffraction region

No abstract available