Five chloropentaaryloxycyclotriphosphazene derivatives were synthesized by the reaction of hexachlorocyclotriphosphazene with potassium phenoxide in tetrahydrofuran. A satisfactory yield could be ...obtained when a 5.1
:
1(KOC
6
H
4
R
:
P
3
N
3
Cl
6
) molar ratio was used. The new compounds were characterized by IR,
1
H NMR,
31
P NMR,
13
C NMR, and ESI-MS, and for two of them by HR-MS.
Photoionization of the rubidium (Rb) atoms cooled in a magneto-optical trap, characterized by the coexistence of the ground 5\(S_{1/2}\) and the excited 5\(P_{3/2}\) states, is investigated ...experimentally and theoretically with the 400 nm femtosecond laser pulses at intensities of \(I=3\times10^9\) W/cm\(^2\) - \(4.5\times10^{12}\) W/cm\(^2\). Recoil-ion momentum distribution (RIMD) of Rb\(^+\) exhibits rich ring-like structures and their energies correspond to one-photon ionization of the 5\(P_{3/2}\) state, two-photon and three-photon ionizations of the 5\(S_{1/2}\) state, respectively. With the increasing of \(I\), we find that experimental signals near zero-momentum (NZM) in RIMDs resulted from the 5\(P_{3/2}\) state enhance dramatically and its peaked Rb\(^+\) momenta dwindle obviously while that from the 5\(S_{1/2}\) state is maintained. Meanwhile, the ion-yield ratio of the 5\(S_{1/2}\) over the 5\(P_{3/2}\) states varies from \(I\) to \(I^{1.5}\) as \(I\) increases. These features indicate a transition from perturbative ionization to strong-perturbative ionization for the 5\(P_{3/2}\) state. Numerical simulations by solving the time-dependent Schr\"odinger equation (TDSE) can qualitatively explain the measurements of RIMD, photoion angular distributions, as well as ion-yield ratio. However, some discrepancies still exist, especially for the NZM dip, which could stem from the electron-electron correlation that is neglected in the present TDSE simulations since we have adopted the single-active-electron approximation.
Employing recent developed magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS) combining cold atom, strong laser pulse, and ultrafast technologies, we study momentum distributions of the ...multiply ionized cold rubidium (Rb) induced by the elliptically polarized laser pulses (35 fs, \(1.3 \times 10^{15}\) W/cm\(^2\)). The complete vector momenta of Rbn+ ions up to charge state n = 4 are recorded with extremely high resolution (0.12 a.u. for Rb\(^+\)). Variations of characteristic multi-bands displayed in momentum distributions, as the ellipticity varies from the linear to circular polarization, are interpreted qualitatively with the classical over-barrier ionization model. Present momentum spectroscopy of cold heavy alkali atoms presents novel strong-field phenomena beyond the noble gases.
We perform high-resolution measurements of momentum distribution on Rb\(^{n+}\) recoil ions up to charge state \(n=4\), where laser-cooled rubidium atoms are ionized by femtosecond elliptically ...polarized lasers with the pulse duration of 35 fs and the intensity of 3.3\(\times\)10\(^{15}\) W/cm\(^2\) in the over-barrier ionization (OBI) regime. The momentum distributions of the recoil ions are found to exhibit multi-band structures as the ellipticity varies from the linear to circular polarizations. The origin of these band structures can be explained quantitatively by the classical OBI model and dedicated classical trajectory Monte Carlo simulations with Heisenberg potential. Specifically, with back analysis of the classical trajectories, we reveal the ionization time and the OBI geometry of the sequentially released electrons, disentangling the mechanisms behind the tilted angle of the band structures. These results indicate that the classical treatment can describe the strong-field multiple ionization processes of alkali atoms.
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