Sequential versus nonsequential two-photon double ionization of the D2 molecule at 38 eV

ABSTRACT: A simple theoretical model is used to interpret recent experimental results for two-photon double ionization (DI) of D2 at 38 eV. We show that the measured kinetic energy distribution associated with emission of two protons can be interpreted as a sum of two processes: a sequential and an instantaneous absorption of the two incident photons. These processes lead to peaks in di erent regions of the spaectrum

Sequential and Direct Two-Photon Double Ionization of D₂ at Flash

Sequential and direct two-photon double ionization (DI) of D2 molecule is studied experimentally and theoretically at a photon energy of 38.8 eV. Experimental and theoretical kinetic energy releases of D++D+fragments, consisting of the contributions of sequential DI via the D2+(1sσg) state and direct DI via a virtual state, agree well with each other

Quantum-Phase Resolved Mapping of Ground-State Vibrational D2 Wave Packets via Selective Depletion in Intense Laser Pulses

Applying 7 fs pump-probe pulses (780 nm, 4×1014 W/cm2) we observe electronic ground-state vibrational wave packets in neutral D2 with a period of T=11.101(70) fs by following the internuclear separation (R-)dependent ionization with a sensitivity of Delta<R><=0.02 Å. The absolute phase of the wave packet's motion provides evidence for R-dependent depletion of the ground state by nonlinear ionization, to be the dominant preparation mechanism. A phase shift of about pi found between pure ionization (D2+) and dissociation (D++D) channels opens a pathway of quantum control

Fragmentation of molecules studied with laser-induced Coulomb explosion imaging and femtosecond pump-probe experiments

We report on the experimental realisation of time-resolved coincident Coulomb explosion imaging of H2-fragmentation in 1014 W/cm2 laser fields. Combining a high-resolution 'reaction microscope' and a fs pump-probe setup, we map the motion of wave packets dissociating via one- or two-photon channels, respectively, and observe two region of enhanced ionization in accordance with earlier theoretical predictions. The long-term interferometric stability of our system allows us to extend pump-probe experiments into the region of overlapping pulses, which offers new possibilities for the manipulation of ultrafast molecular fragmentation dynamics

Real-time observation of vibrational revival in the fastest molecular system

After preparing a coherent vibrational wave packet in the hydrogen molecular ion by ionizing neutral H2 molecules with a 6.5 fs, 760 nm laser pulse at 3 × 1014 W/cm2, we map its spatio-temporal evolution by the fragmentation induced with a second 6.5 fs laser pulse of doubled intensity. In this proof-of-principle experiment, we visualize the oscillations of this most fundamental molecular system, observe a dephasing of the vibrational wave packet and its subsequent revival. Whereas the experimental data exhibit an overall qualitative agreement with the results of a simple numerical simulation, noticeable discrepancy is found in the characteristic revival time. The most likely reasons for this disagreement originate from the simplifications used in the theoretical model, which assumes a Franck–Condon transition induced by the pump pulse with subsequent field-free propagation of the Click to view the MathML source vibrational wave packet, and neglects the influence of the rotational motion

Single ionization of atoms in intense laser pulses: Evolution from multiphoton to tunnel ionization

We present results of high resolution fully differential measurements on single ionization of He, Ne, and Ar by 7-25 fs linearly polarized 800nm laser pulses at intensities of up to 2.1015 W/cm2. Using a 'Reaction-Microscope' we were able to trace signatures of multiphoton ionization deep into the tunnelling regime. Surprisingly, in the low-energy electron spectra we observed several features (absence of the ponderomotive shifts, splitting of the peaks, their degeneration for few-cycle laser pulses) typical for resonantly-enhanced ionization. Other remarkable features, as the sharp cusp-like momentum distributions in the direction perpendicular to the laser field or the observed minima at zero longitudinal momentum for He and Ne, can be reproduced by semiclassical models, where the electron motion in the combined laser and Coulomb field is treated classically after the tunnelling

Atomic Collisions Studied with Reaction Microscopes

An overview of results obtained with reaction microscopes is given. Due to the enormous diversity and amount of experimental results obtained with this technique, covering many different areas of collision physics, only a few and only the very recent results in the fields of charged particle-atom and intense laser-atom interactions will be presented here. For more comprehensive overviews the reader is referred to recent reviews [1,2]