We have measured absolute triple differential cross sections for photo-double ionization of helium at 20 eV excess. The measurement covers the full ranges of energy sharing and emission angles of the two photoelectrons. We compare our data for selected geometries with the convergent close-coupling (CCC) calculations as well as 2SC calculations by Pont and Shakeshaft and 3C calculations by Maulbetsch and Briggs. In terms of the absolute magnitude and the trend in the shapes of the triple differential cross section for different geometries we find good agreement of the CCC and published 2SC calculations with our measurement, though differences with respect to the observed shape of individual patterns still exist.
We present the results of the detailed experimental study of multiple ionization of Ne and Ar by 25 and 7 fs laser pulses. For Ne the highly correlated "instantaneous" emission of up to four electrons is triggered by a recollisional electron impact, whereas in multiple ionization of Ar different mechanisms, involving field ionization steps and recollision-induced excitations, play a major role. Using few-cycle pulses we are able to suppress those processes that occur on time scales longer than one laser cycle.
Recoil-ion momentum distributions for two-photon double ionization of He and Ne (@! 44 eV) have been recorded with a reaction microscope at FLASH (the free-electron laser at Hamburg) at an intensity of 1 10 14 W=cm 2 exploring the dynamics of the two fundamental two-photon-two-electron reaction pathways, namely, sequential and direct (or nonsequential) absorption of the photons. We find strong differences in the recoil-ion momentum patterns for the two mechanisms pointing to the significantly different two-electron emission dynamics and thus provide serious constraints for theoretical models. DOI: 10.1103/PhysRevLett.101.073003 PACS numbers: 32.80.Rm, 41.60.Cr, 42.65.ÿk Since Einstein's revolutionary explanation of the photoelectric effect in 1905, the breakup of bound systems as a result of their interaction with single light quanta -the photons-has remained in the very focus of interest in experimental and theoretical physics as well as in chemistry and biology as one of the most fundamental reactions occurring in nature. Whenever there is more than one electron actively involved in the photoabsorption process, however, one faces serious problems in calculations as well as in measurements, even if only a single photon is absorbed at a time. Thus, the simplest situation where two electrons emerge from the He atom has numerically been solved only within the last decade when fully differential experimental cross sections have become available (see [1] for a review).Keeping the simple He target but increasing the number of photons, as, e.g., in strong-field double ionization at optical frequencies needing more than 50 quanta, still represents a serious challenge for computations (see, e.g., [2]). Likewise, kinematically complete experiments for this regime have been reported only within the last two months [3,4]. Also for the process of double ejection by Compton scattering, the comparison of experiment and theory does not go beyond the level of total cross sections [5].In this Letter we report the first differential measurement, recoil-ion momentum distributions, for the most basic nonlinear two-electron light-matter interaction, where two vacuum ultraviolet photons (44 eV each) ''simultaneously'' remove two electrons from He. The results are compared to the double ionization of Ne, where a sequential, stepwise absorption pathway with intermediate relaxation to a bound state of the Ne ion is energetically allowed. Vastly different momentum distributions are observed for both reactions and compared with theoretical predictions. Since the measured recoil-ion momentum spectra reflect the sum-momentum distributions of the emitted electrons and thus yield first information about the relative emission angles and the energy sharing between both electrons for different nonlinear processes, the data provide stringent test grounds for theoretical models. The experiments became feasible by exploiting a unique combination of modern multiparticle momentum imaging technique, ''reaction microscope' ' [6], and a novel light ...
Abstract. We use correlated electron-ion momentum measurement to investigate laser induced non-sequential double ionization of Ar and Ne. Light intensities are chosen in a regime at and below the threshold where, within the rescattering model, electron impact ionization of the singly charged ion core is expected to become energetically forbidden. Yet, we find Ar ++ ion momentum distributions and an electron-electron momentum correlation indicative of direct impact ionization. Within the quasistatic model this may be understood by assuming that the electric field of the light wave reduces the ionization potential of the singly charged ion core at the instant of scattering. The width of the projection of the ion momentum distribution onto an axis perpendicular to the light beam polarization vector is found to scale with the square root of the peak electric field strength in the light pulse. A scaling like this is not expected from the phase space available after electron impact ionization. It may indicate that the electric field at the instant of scattering is usually different from zero and determines the transverse momentum distribution. A comparison of our experimental results with several theoretical results is given.
The dynamics of He double ionization by 2 keV electron impact is studied experimentally for a momentum transfer of 0.6 a.u. at excess energies of 10 and 40 eV. Complete sets of fivefold differential cross sections are presented for all electron emission angles in coplanar geometry. Contributions beyond the first Born approximation are identified comparing experimental data with first order convergent close-coupling calculations which are in considerably better agreement with the present experiment than with the earlier measurement of Kheifets et al. [J. Phys. B 32, 5047 (1999)].
By combining carrier-envelope phase (CEP) stable light fields and the traditional method of optical pump-probe spectroscopy we study electron localization in dissociating H2(+) molecular ions. Localization and localizability of electrons is observed to strongly depend on the time delay between the two CEP-stable laser pulses with a characteristic periodicity corresponding to the oscillating molecular wave packet. Variation of the pump-probe delay time allows us to uncover the underlying physical mechanism for electron localization, which are two distinct sets of interfering dissociation channels that exhibit specific temporal signatures in their asymmetry response.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.