Modified effective-range theory (MERT) was developed in the 1960s to describe electron and positron scattering from atoms. The theory was frequently used to extrapolate measured total cross sections down to the zero-energy region, which is inaccessible experimentally. However, the applicability of the model was usually limited to the very low energy range where experimental data to be extrapolated are rare. We have proposed [Idziaszek and Karwasz, Phys. Rev. A 73, 064701 (2006)] a different way of employing MERT by exploiting the properties of an analytical solution of the Schrödinger scattering equation with the long-range polarization potential. This alternative approach allows the validity of MERT to be extended to higher energies. At present we are applying this procedure for electron and positron scattering on He, H 2 , Ar, and CH 4 . The scattering amplitude and the effective-range parameters for s and p partial waves are obtained through a fitting inversion procedure applied to integral cross sections spanning most or all of the elastic region. The derived parameters are then used to obtain differential and momentum transfer cross sections; the agreement with experiments is very good.
Quest for photo-stable amorphous thin films in ternary Ge(x)As(y)Se(100-x-y) chalcogenide system is reported. Studied layers were fabricated using pulsed laser deposition technique. Scanning electron microscope with energy dispersive X-ray analyzer, Raman scattering spectroscopy, transmittance measurements, variable angle spectroscopic ellipsometry, and non-linear imaging technique with phase object inside the 4f imaging system were employed to characterize prepared thin films. Their photo-stability/photo-induced phenomena in as-deposited and relaxed states were also investigated, respectively. In linear regime, we found intrinsically photo-stable relaxed layers within Ge(20)As(20)Se(60) composition. This composition presents also the highest optical damage threshold under non-linear optical conditions.
Abstract. Electron-scattering cross sections in methane are analysed in the very-low energy region. The correspondence between integral elastic, elastic differential and momentum transfer cross sections is checked via a novel approach to modified effective range theory, in order to determine the depth and position of the Ramsauer-Townsend minimum. Phase shifts of the two lowest partial waves are obtained explicitly and parameterized by four coefficients with the physical meaning of the scattering lengths and the effective ranges. Using recent experiments on vibrational cross sections performed over an extended (0-180• ) angular range and comparing several theories, an agreement within 10% has been obtained between experimental total and present summed (elastic + vibrational) cross sections in the whole 0.1-2.0 eV energy range. An additional check for consistency is done using two-term Boltzmann analysis to derive electron diffusion coefficients. Calculated drift velocities and transversal diffusion coefficients at 0-10 Td reduced electric field agree within 5% with experiments.
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