Imaging an aligned polyatomic molecule with laser-induced electron diffraction.

Michael G Pullen,Claus Dieter Schröter,Jens Biegert,Joachim Ullrich,Anh-Thu Le,Arne Senftleben,C D Lin,Matthias Baudisch,Michaël Hemmer,Robert Moshammer,Benjamin Wolter

doi:10.1038/ncomms8262

Abstract

Laser-induced electron diffraction is an evolving tabletop method that aims to image ultrafast structural changes in gas-phase polyatomic molecules with sub-Ångström spatial and femtosecond temporal resolutions. Here we demonstrate the retrieval of multiple bond lengths from a polyatomic molecule by simultaneously measuring the C–C and C–H bond lengths in aligned acetylene. Our approach takes the method beyond the hitherto achieved imaging of simple diatomic molecules and is based on the combination of a 160 kHz mid-infrared few-cycle laser source with full three-dimensional electron–ion coincidence detection. Our technique provides an accessible and robust route towards imaging ultrafast processes in complex gas-phase molecules with atto- to femto-second temporal resolution.

Highlights

Laser-induced electron diffraction is an evolving tabletop method that aims to image ultrafast structural changes in gas-phase polyatomic molecules with sub-Ångstrom spatial and femtosecond temporal resolutions
Ultrafast electron diffraction (UED) is capable of resolving atomic positions with sub-Ångstrom resolution[6], the achievable temporal resolution is currently limited to hundreds of femtoseconds mainly due to Coulomb repulsion in the electron bunch
Spatial resolutions of 0.05 Å were reported, which were sufficient to image a 0.1 Å contraction of the simple O2 molecule during the B5 fs it takes an electron to rescatter. This result established the potential of Laser-induced electron diffraction (LIED) as a dynamical imaging technique with subÅngstrom spatial and few-femtosecond temporal resolutions

Summary

Introduction

Laser-induced electron diffraction is an evolving tabletop method that aims to image ultrafast structural changes in gas-phase polyatomic molecules with sub-Ångstrom spatial and femtosecond temporal resolutions. The challenge lies in simultaneously fulfilling the extremely stringent conditions for LIED in order to extract structural information; these are as follows: (i) achieving high recollision energies despite a small fraction of target ionization, (ii) achieving core penetrating collisions and sufficient momentum transfer with the scattered electron, (iii) driving recollision in the quasi-static regime to enable extraction of fieldfree diffraction data from the photoelectron momentum spectra When these conditions are met, the method of molecular structure retrieval is similar to conventional electron or X-ray diffraction, with the added benefit of femtosecond temporal resolution of the driving laser. This result established the potential of LIED as a dynamical imaging technique with subÅngstrom spatial and few-femtosecond temporal resolutions

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Conclusion