Quadrupolar relaxation in (KBr)1−x(KCN)x<

Abstract

Brillouin scattering was used to study the dynamic properties of the mixed crystals (KBr), "(KCN)". By analyzing the frequencies and linewidths of the T2g-symmetry phonon, we were able to determine the cyanide quadrupolar relaxation rate as a function of temperature in the paraelastic regime. We found that this relaxation frequency is proportional to exp( -1/T), rather than proportional to the square root of temperature (&T), as assumed in Michel's random-field theory. Modifying this theory by incorporating the observed temperature dependence of the relaxation rate improves the agreement with experimental data but is still not adequate. The hierarchically constrained relaxation model of Palmer et al. , on the other hand, does provide a phenomenological explanation for our data. In addition, we have determined the value of the random-field strength in these mixed systems.

Nonsequential Two-Photon Double Ionization of Atoms: Identifying the Mechanism

“…However, it is only during the last 15 years or so, that advances in theory, modeling and experiment have enabled scientists to gain a deeper insight into the role of electron correlations in this ionization process [1][2][3][4][5]. The corresponding problem of two-photon double ionization of helium, in the photon energy interval between 39.4 and 54.4 eV, is an outstanding quantum mechanical problem that has been, and still is, subject to intense research worldwide, both theoretically [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and experimentally, employing state-of-the-art high-order harmonic [20][21][22] and free-electron (FEL) light sources [23,24]. Despite all the interest and efforts that have been put into this research, major fundamental issues remain unresolved.…”

Two-photon double ionization ofH2in intense femtosecond laser pulses

“…This is qualitatively similar to those of the atomic target through 1 S e → 1 P o → 1 S e or 1 S e → 1 P o → 1 D e . An interference effect between the open channels 1 Σ g and 1 ∆ g in H 2 is evident, as it is in the helium atom between the 1 S e and 1 D e channels [12]. Such interference cannot be observed in the parallel orientation, where only one channel is open.…”

Spectral data for doubly excited states of helium with non-zero total angular momentum

“…However, due to the difficulty to extract physical information from this grid approach and its high requirements concerning computational resources, an accurate spectral approach to this problem becomes even more desirable. Further correlation effects have been observed in two-photon double ionization by strong XUV pulses where almost no experimental data is available and theoretical predictions [20][21][22][23][24][25][26][27][28] for the two-photon double ionization cross section among themselves deviate by orders of magnitude.…”