Recoil-ion and electron momentum spectroscopy: reaction-microscopes

Abstract

Recoil-ion and electron momentum spectroscopy is a rapidly developing technique that allows one to measure the vector momenta of several ions and electrons resulting from atomic or molecular fragmentation. In a unique combination, large solid angles close to π Microccopes -the "bubble chambers of atomic physics" -mark the decisive step forward to investigate many-particle quantum-dynamics occurring when atomic and molecular systems or even surfaces and solids are exposed to time-dependent external electromagnetic fields.The present review concentrates on just these latest technical developments and on at least four new classes of fragmentation experiments that have emerged within about the last five years. First, multi-dimensional images in momentum space brought unprecedented information on the dynamics of single-photon induced fragmentation of fixed-in-space molecules and on their structure. Second, a break-through in the investigation of highintensity short-pulse laser induced fragmentation of atoms and molecules has been achieved by using Reaction Microccopes. Third, for electron and ion-impact, the investigation of twoelectron reactions has matured to a state such that first fully differential cross sections (FDCS) are reported. Forth, comprehensive sets of FDCS for single ionisation of atoms by ion-impact, the most basic atomic fragmentation reaction, brought new insight, a couple of surprises and unexpected challenges to theory at keV to GeV collision energies. In addition, a brief summary on the kinematics is provided at the beginning. Finally, the rich future potential of the method is shortly envisaged.2

Attosecond tracing of correlated electron-emission in non-sequential double ionization

“…The electric field of the laser pulse can be approximated as E(t) = E 0 cos 2 (t/τ) cos(ωt + φ), where E 0 is the field amplitude, ω is the carrier frequency, τ is the pulse duration, and φ is the CEP. Combining a reaction microscope (REMI) 20 with a newly developed phase-tagging technique 21 , we obtained the CEP of the laser pulse for each and every ionization event 22 recorded with the REMI. The laser was focussed to a maximum instantaneous intensity of I 0 = cε 0 E 0 2 = (3.0 ± 0.6)×10 14 W cm − 2 into a cold supersonic gas jet of neutral argon atoms located in the centre of the REMI.…”

“…A fraction (11 µJ) of the remaining part of the laser beam is focussed with a spherical mirror (f = 25 cm) into a well-localized (1 mm width) and cold supersonic gas jet of neutral argon atoms in the centre of a REMI 20 . Ions and electrons created in the laser focus (~40 µm diameter) are extracted by a weak electric field towards microchannel plate (MCP) detectors equipped with delay line anodes for position readout at the left and right side of the instrument, respectively.…”

Reconstruction and control of a time-dependent two-electron wave packet

“…2f) clearly show that the two-electron motion in the reconstructed doubly excited wave packet is highly correlated. Direct experimental observation of such concerted dynamics requires the use of coincidence techniques [25][26][27] and represents a major future goal. At higher intensities (Methods -Intensity Calibration‖; Extended Data Fig.…”

“…Ref. 25) for direct measurements of the spatial shape of two-(or multi-)electron wave packets as a function of time in the attosecond domain. The extracted state-dependent phases υ n (I) will allow further insight into the coupling among two electrons and how they, collectively or cooperatively, acquire dynamical phases υ n (I) = ∫ΔE n (t)dt, by time-dependent and state(n)-dependent energy-level shifts ΔE n (t) (e.g.…”

Line ratios for soft-x-ray emission following charge exchange betweenO8+and Kr

“…The present study serves as an important benchmark for resolving angular momentum quantum states and subsequent decay schemes for theory when both single and multiple electron capture are present. This is a challenge for other experimental measurements, even the well-developed cold target recoil ion momentum spectroscopy [40]. …”