Narrow Results

In a previous paper, we showed theoretically that the total cross-section of the top-quark pair production by electron–positron annihilation is strongly reduced by the presence of a circularly polarized laser field. In this paper, we present the result for the case of a linearly polarized laser field. This time, the total cross-section is significantly enhanced by the laser field.

Electron-impact excitation of tungsten ions $W^{q+}(q=40-43)$ has been studied using the fully relativistic distorted wave (RDW) theory. The excitation cross-sections of selected electric dipole allowed transitions of these ions to be determined for the incident electron energies from the excitation threshold to 20 keV. Further, the calculated cross-section results are fitted with an analytical expression for direct applications in plasma modeling. In addition, using the density matrix theory, the linear polarization of the photons emitted from the excited tungsten ions when decay to their respective ground states is presented.

Measurements of emission cross sections for the ${\mathrm{\text{O}}}^{+}-{\mathrm{\text{N}}}_2$ collision system with the incident beam of 1–10 keV ${\mathrm{\text{O}}}^{+}$ in the ground ${\mathrm{\text{O}}}^{+}{(}^{4}S$) and metastable ${\mathrm{\text{O}}}^{+}{(}^{2}D)$ and ${\mathrm{\text{O}}}^{+}{(}^{2}P)$ states are reported. The emission cross section induced by incident ions in the metastable state ${\mathrm{\text{O}}}^{+}{(}^{2}P)$ is much larger than that for the ground ${\mathrm{\text{O}}}^{+}{(}^{4}S)$ state. The emission cross section of ${\mathrm{\text{N}}}_2^{+}$ ion for $(0,0)$, $(0,1)$, and $(1,2)$ bands system is measured and the ratio of intensities for these bands is established as $10:3:1.$ It is shown that the cross sections for the ${\mathrm{\text{N}}}^{{+}^{\ast }}$ ions emissions in the dissociative charge exchange processes increase with the increase of the incident ion energy. The energy dependence of the emission cross section of the band $(0,0)$$\lambda =391.4$ nm of the first-negative band system of the ${\mathrm{\text{N}}}_2^{+}$ and degree of linear polarization of emission in ${\mathrm{\text{O}}}^{+}-{\mathrm{\text{N}}}_2$ collision are measured for the first time. An influence of an admixture of the ion metastable state on a degree of linear polarization is revealed. The mechanism of the processes realized during collisions of ground and metastable oxygen ions on molecular nitrogen have been established. It is demonstrated that for ${\mathrm{\text{O}}}^{+}-{\mathrm{\text{N}}}_2$ collision system the degree of linear polarization by metastable ${\mathrm{\text{O}}}^{+}{(}^{2}P)$ ions is less compared to those that are in the ground ${\mathrm{\text{O}}}^{+}{(}^{4}S)$ state and the sign of emission of degree of linear polarization of excited molecular ions does not change.

Excited states in ${}^{126,128}$Xe were populated via ${}^{122}$Sn(⁹Be, 5n$\gamma$) and ${}^{122}$Sn(⁹Be, 3n$\gamma$) fusion-evaporation reactions, respectively, at a beam energy of 48MeV. The electromagnetic (electric or magnetic) nature and multipolarity of some inter-band $\gamma$ rays are determined from linear polarization and angular correlation measurements. Re-measured/newly measured linear polarization asymmetry helps to assign the parity of 2302-keV (${}^{126}$Xe)/2228-keV (${}^{128}$Xe) $I^{\pi }=5^{-}$ state unequivocally.

With the advent of modern synchrotron radiation facilities, fluorescence-detected X-ray absorption spectroscopy (XAS) has proven its capability as a highly sensitive local structural tool. Previous applications have been limited to dilute systems and thin films where the absorption of incoming incidence X-ray and outgoing fluorescence X-ray can be neglected. In this chapter we describe unconventional applications beyond this criterion, which are made possible by improving detection efficiency by orders of magnitude combining a high flux insertion devices and highly efficient detectors. In the first application, the non-equilibrium local structure of photo-induced phase of Fe(II) spin crossover complex, [Fe(2-pic)₃]Cl₂EtOH (2-pic=2-aminomethyl pyridine), was investigated under laser illumination. The results indicated no symmetry breaking of FeN₆ clusters upon spin-state switching, establishing the origin of new Raman lines as unrelaxed “frozen-in” distorted outer ligand molecules. Secondly, we demonstrate that polarization-dependent XAS is obtained with a high quality for high temperature superconducting (HTSC) single crystals. The results of temperature-dependent local lattice study on high-quality single crystal of LaSr- CuO revealed doping-induced local lattice distortion $T_d^{\max }$ that maximizes at the superconducting critical temperature $T_c^{\max }$, indicating the strong intimacy of HTSC with local lattice, casting doubts to the purely electronic pairing mechanisms that ignore the contribution of lattice. Lastly, we describe that, combining a microfluidic cell with a fluorescence detection, position-dependent XAS provides time-dependent XAS for dilute systems. The application to CdSe nanocrystal formation demonstrated that such an approach would allow in situ studies on the structural evolution of intermediate state of nanocluster formation known as puzzling state, i.e. “monomers”, in association with molecular orbital calculations. Because of a limited space, unconventional applications are briefly described in this chapter but it could be sufficient to expect more outputs from the 4^th generation synchrotron facilities that would allow higher brilliance and a smaller focus size because the methodology described here is strongly dependent on synchrotron instrumentation.