Angular anisotropy parameters and recoil-ion momentum distribution in two-photon double ionization of helium

We present convergent-close-coupling (CCC) calculations of the angular anisotropy parameters β2,β4 and the recoil ion momentum distribution dσ∕dp in two-photon double ionization (TPDI) of helium. In a stark contrast to single-photon double ionization (SPDI), where the β2 parameter varies widely changing the angular distribution from isotropic to nearly dipole for slow and fast photoelectrons, respectively, the β parameters for TPDI show very little change. The angular distribution of the recoil ion is fairly isotropic in TPDI as opposed to a strong alignment with the polarization of light in SPDI

A note on the existence of non-monotone non-oscillating wavefronts

In this note, we present a monostable delayed reaction-diffusion equation with the unimodal birth function which admits only non-monotone wavefronts. Moreover, these fronts are either eventually monotone (in particular, such is the minimal wave) or slowly oscillating. Hence, for the Mackey-Glass type diffusive equations, we answer affirmatively the question about the existence of non-monotone non-oscillating wavefronts. As it was recently established by Hasik {\it et al.} and Ducrot {\it et al.}, the same question has a negative answer for the KPP-Fisher equation with a single delay.Comment: 11 pages, 3 figures, submitte

Angular anisotropy parameters for sequential two-photon double ionization of helium

We evaluate photoelectron angular anisotropy β parameters for the process of sequential two-photon double electron ionization of helium within the lowest-order time-independent perturbation theory. Our results indicate that for photoelectron energies outside the interval (Eslow,Efast), where Eslow=ω−VHe+ and Efast=ω−VHe, there is a considerable deviation from the dipole angular distribution, thus indicating the effect of electron correlation

Complete characterization of double photoionization processes

We analyze correlated photoelectron spectra of single-photon two-electron ionization [double photoionization (DPI)] of helium to reconstruct the phase of the spectral amplitude of this process. The phase can be reconstructed reliably in a wide range of photoelectron momenta, thus allowing one to retrieve information about the wave function of the DPI process and its temporal evolution. Our simulation indicates that the proposed phase reconstruction technique can be applied in experiment to trace dynamics of the DPI process with attosecond precision

Stable periodic solutions in scalar periodic differential delay equations

summary:A class of nonlinear simple form differential delay equations with a $T$-periodic coefficient and a constant delay $\tau >0$ is considered. It is shown that for an arbitrary value of the period $T>4\tau -d_0$, for some $d_0>0$, there is an equation in the class such that it possesses an asymptotically stable $T$-period solution. The periodic solutions are constructed explicitly for the piecewise constant nonlinearities and the periodic coefficients involved, by reduction of the problem to one-dimensional maps. The periodic solutions and their stability properties are shown to persist when the nonlinearities are “smoothed” at the discontinuity points

Extraction of the attosecond time delay in atomic photoionization using the soft-photon approximation

We use the soft-photon approximation to extract the Wigner time delay from atomic two-color photoionization experiments. Unlike the strong-field approximation, the present method does not require introduction of the Coulomb-laser coupling corrections an

Transverse electron momentum distribution in strong field ionization: Transition from tunneling to over the barrier ionization regimes

We study transverse electron momentum distribution (TEMD) in strong field atomic ionization driven by laser pulses with varying ellipticity. We show, that the TEMD in the tunneling and over the barrier ionization regimes evolves in a qualitatively different way when the ellipticity parameter describing polarization state of the driving laser pulse increases