Multiple ionization of neon, argon and xenon in a high-intensity Ti:Sapphire laser field (λ = 800 nm) has been studied. Ion yield curves of xenon versus laser intensity have been obtained for the first six charges. Curves of charges 2+ to 6+ present obvious structures which can be attributed to the occurrence of non-sequential ionization processes. Also, comparison of the ion yields of the first three charges of Ar with previously obtained results inside a different laser field (Nd:Glass laser λ = 1053 nm, τ = 600 fs) indicates that non-sequential ionization is strongly wavelength dependent.

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Extensive X-ray and neutron scattering experiments and additional transmission electron microscopy results reveal the partial decomposition of Nd2−xCexCuO 4±δ (NCCO) in a low-oxygenfugacity environment such as that typically realized during the annealing process required to create a superconducting state. Unlike a typical situation in which a disordered secondary phase results in diffuse powder scattering, a serendipitous match between the in-plane lattice constant of NCCO and the lattice constant of one of the decomposition products, (Nd,Ce)2O3, causes the secondary phase to form an oriented, quasi-two-dimensional epitaxial structure. Consequently, diffraction peaks from the secondary phase appear at rational positions (H, K, 0) in the reciprocal space of NCCO. Additionally, because of neodymium paramagnetism, the application of a magnetic field increases the low-temperature intensity observed at these positions via neutron scattering. Such effects may mimic the formation of a structural superlattice or the strengthening of antiferromagnetic order of NCCO, but the intrinsic mechanism may be identified through careful and systematic experimentation. For typical reduction conditions, the (Nd,Ce)2O3 volume fraction is ∼ 1%, and the secondary-phase layers exhibit long-range order parallel to the NCCO CuO2 sheets and are 50 − 100 A thick. The presence of the secondary phase should also be taken into account in the analysis of other experiments on NCCO, such as transport measurements.

Using 200 fs, 800 nm Ti:sapphire laser pulses to ionize noble atom gases, the ion versus intensity curves of these gases were obtained. By comparing the experimental curves with those obtained using different theoretical ionization rates, it was found that the inclusion of the effects on the ionization rate of the long-range Coulomb potential of the parent ion through quasi-classical perturbation theory (as proposed by Perelomov et al and Krainov) gives a rather good overlap with the experimental results.

X-ray scattering measurements of the low-temperature structure of La(1-x)Sr(1+x)MnO(4) ( 0.33< or =x< or =0.67) indicate the existence of three distinct regions: a disordered phase (x<0.4), a charge-ordered phase (x> or =0.5), and a mixed phase (0.4< or =x<0.5). For x>0.5, the modulation vector associated with the charge order is incommensurate with the lattice and depends linearly on the concentration of e(g) electrons. The primary superlattice reflections are strongly suppressed along the modulation direction and the higher harmonics are weak, implying the existence of a largely transverse and nearly sinusoidal structural distortion, consistent with a charge-density wave of the e(g) electrons.