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

Pullen MG, Wolter B, Le AT, Baudisch M, Hemmer M, Senftleben A, Schröter CD, Ullrich J, Moshammer R, Lin CD, Biegert J - Nat Commun (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, Castelldefels (Barcelona) 08860, Spain.

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.

No MeSH data available.


Laser-induced electron diffraction from aligned C2H2 molecules using a mid-infrared OPCPA source and a reaction microscope.The cartoon film shows the procedure. (a) The C2H2 molecules are pre-aligned by focusing the 1.7 μm pump pulse (blue) into a molecular jet. (b) The 3.1 μm pulse (red) is used to generate high-energy electrons that subsequently rescatter off the parent ion. (c) The rescattered electrons carry structural information of the parent ion that is contained in the detected angular momentum distributions. The anticollinear electric (E) and magnetic (B) fields guide the charged fragments towards opposing position-sensitive detectors.
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f1: Laser-induced electron diffraction from aligned C2H2 molecules using a mid-infrared OPCPA source and a reaction microscope.The cartoon film shows the procedure. (a) The C2H2 molecules are pre-aligned by focusing the 1.7 μm pump pulse (blue) into a molecular jet. (b) The 3.1 μm pulse (red) is used to generate high-energy electrons that subsequently rescatter off the parent ion. (c) The rescattered electrons carry structural information of the parent ion that is contained in the detected angular momentum distributions. The anticollinear electric (E) and magnetic (B) fields guide the charged fragments towards opposing position-sensitive detectors.

Mentions: Clearly, versatile laboratory-scale tabletop methods that provide the combined spatial and temporal resolutions would signify a breakthrough, especially for the imaging of gas-phase molecular dynamics. Laser-induced electron diffraction (LIED) is such a method and is based on probing an objects structure using its own electrons that are rescattered during strong-field-induced recollisions151617. This process is depicted in Fig. 1 where the longitudinal and transverse momenta are defined as k//=ky and , respectively. Coherent subcycle elastic scattering of the electron wavepacket with attosecond (single pulse) to femtosecond (pulse train) resolution retains structural information of the ionic species in the resultant diffraction pattern18192021. 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 field-free 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. In general, state of the art near-infrared lasers cannot fulfil these combined conditions, however, investigations have still been undertaken for homonuclear diatomic molecules such as O2 (ref. 19). Recently, these conditions were satisfied with ∼2 μm lasers and structural retrieval of N2 and O2 molecules was demonstrated2223. 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 ∼5 fs it takes an electron to rescatter. This result established the potential of LIED as a dynamical imaging technique with sub-Ångström spatial and few-femtosecond temporal resolutions.


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

Pullen MG, Wolter B, Le AT, Baudisch M, Hemmer M, Senftleben A, Schröter CD, Ullrich J, Moshammer R, Lin CD, Biegert J - Nat Commun (2015)

Laser-induced electron diffraction from aligned C2H2 molecules using a mid-infrared OPCPA source and a reaction microscope.The cartoon film shows the procedure. (a) The C2H2 molecules are pre-aligned by focusing the 1.7 μm pump pulse (blue) into a molecular jet. (b) The 3.1 μm pulse (red) is used to generate high-energy electrons that subsequently rescatter off the parent ion. (c) The rescattered electrons carry structural information of the parent ion that is contained in the detected angular momentum distributions. The anticollinear electric (E) and magnetic (B) fields guide the charged fragments towards opposing position-sensitive detectors.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4491169&req=5

f1: Laser-induced electron diffraction from aligned C2H2 molecules using a mid-infrared OPCPA source and a reaction microscope.The cartoon film shows the procedure. (a) The C2H2 molecules are pre-aligned by focusing the 1.7 μm pump pulse (blue) into a molecular jet. (b) The 3.1 μm pulse (red) is used to generate high-energy electrons that subsequently rescatter off the parent ion. (c) The rescattered electrons carry structural information of the parent ion that is contained in the detected angular momentum distributions. The anticollinear electric (E) and magnetic (B) fields guide the charged fragments towards opposing position-sensitive detectors.
Mentions: Clearly, versatile laboratory-scale tabletop methods that provide the combined spatial and temporal resolutions would signify a breakthrough, especially for the imaging of gas-phase molecular dynamics. Laser-induced electron diffraction (LIED) is such a method and is based on probing an objects structure using its own electrons that are rescattered during strong-field-induced recollisions151617. This process is depicted in Fig. 1 where the longitudinal and transverse momenta are defined as k//=ky and , respectively. Coherent subcycle elastic scattering of the electron wavepacket with attosecond (single pulse) to femtosecond (pulse train) resolution retains structural information of the ionic species in the resultant diffraction pattern18192021. 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 field-free 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. In general, state of the art near-infrared lasers cannot fulfil these combined conditions, however, investigations have still been undertaken for homonuclear diatomic molecules such as O2 (ref. 19). Recently, these conditions were satisfied with ∼2 μm lasers and structural retrieval of N2 and O2 molecules was demonstrated2223. 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 ∼5 fs it takes an electron to rescatter. This result established the potential of LIED as a dynamical imaging technique with sub-Ångström spatial and few-femtosecond temporal resolutions.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, Castelldefels (Barcelona) 08860, Spain.

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.

No MeSH data available.