@article{YangGuehrVecchioneetal.2016,
  author    = {Yang, Jie and G{\"u}hr, Markus and Vecchione, Theodore and Robinson, Matthew Scott and Li, Renkai and Hartmann, Nick and Shen, Xiaozhe and Coffee, Ryan and Corbett, Jeff and Fry, Alan and Gaffney, Kelly and Gorkhover, Tais and Hast, Carsten and Jobe, Keith and Makasyuk, Igor and Reid, Alexander and Robinson, Joseph and Vetter, Sharon and Wang, Fenglin and Weathersby, Stephen and Yoneda, Charles and Centurion, Martin and Wang, Xijie},
  title     = {Diffractive imaging of a rotational wavepacket in nitrogen molecules with femtosecond megaelectronvolt electron pulses},
  series = {Nature Communications},
  volume    = {7},
  journal   = {Nature Communications},
  publisher = {Nature Publ. Group},
  address   = {London},
  issn      = {2041-1723},
  doi       = {10.1038/ncomms11232},
  pages     = {9},
  year      = {2016},
  abstract  = {Imaging changes in molecular geometries on their natural femtosecond timescale with sub-Angstrom spatial precision is one of the critical challenges in the chemical sciences, as the nuclear geometry changes determine the molecular reactivity. For photoexcited molecules, the nuclear dynamics determine the photoenergy conversion path and efficiency. Here we report a gas-phase electron diffraction experiment using megaelectronvolt (MeV) electrons, where we captured the rotational wavepacket dynamics of nonadiabatically laser-aligned nitrogen molecules. We achieved a combination of 100 fs root-mean-squared temporal resolution and sub-Angstrom (0.76 angstrom) spatial resolution that makes it possible to resolve the position of the nuclei within the molecule. In addition, the diffraction patterns reveal the angular distribution of the molecules, which changes from prolate (aligned) to oblate (anti-aligned) in 300 fs. Our results demonstrate a significant and promising step towards making atomically resolved movies of molecular reactions.},
  language  = {en}
}
@misc{YangGuehrVecchioneetal.2016,
  author    = {Yang, Jie and Guehr, Markus and Vecchione, Theodore and Robinson, Matthew Scott and Li, Renkai and Hartmann, Nick and Shen, Xiaozhe and Coffee, Ryan and Corbett, Jeff and Fry, Alan and Gaffney, Kelly and Gorkhover, Tais and Hast, Carsten and Jobe, Keith and Makasyuk, Igor and Reid, Alexander and Robinson, Joseph and Vetter, Sharon and Wang, Fenglin and Weathersby, Stephen and Yoneda, Charles and Wang, Xijie and Centurion, Martin},
  title     = {Femtosecond gas phase electron diffraction with MeV electrons},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394989},
  pages     = {19},
  year      = {2016},
  abstract  = {We present results on ultrafast gas electron diffraction (UGED) experiments with femtosecond resolution using the MeV electron gun at SLAC National Accelerator Laboratory. UGED is a promising method to investigate molecular dynamics in the gas phase because electron pulses can probe the structure with a high spatial resolution. Until recently, however, it was not possible for UGED to reach the relevant timescale for the motion of the nuclei during a molecular reaction. Using MeV electron pulses has allowed us to overcome the main challenges in reaching femtosecond resolution, namely delivering short electron pulses on a gas target, overcoming the effect of velocity mismatch between pump laser pulses and the probe electron pulses, and maintaining a low timing jitter. At electron kinetic energies above 3 MeV, the velocity mismatch between laser and electron pulses becomes negligible. The relativistic electrons are also less susceptible to temporal broadening due to the Coulomb force. One of the challenges of diffraction with relativistic electrons is that the small de Broglie wavelength results in very small diffraction angles. In this paper we describe the new setup and its characterization, including capturing static diffraction patterns of molecules in the gas phase, finding time-zero with sub-picosecond accuracy and first time-resolved diffraction experiments. The new device can achieve a temporal resolution of 100 fs root-mean-square, and sub-angstrom spatial resolution. The collimation of the beam is sufficient to measure the diffraction pattern, and the transverse coherence is on the order of 2 nm. Currently, the temporal resolution is limited both by the pulse duration of the electron pulse on target and by the timing jitter, while the spatial resolution is limited by the average electron beam current and the signal-to-noise ratio of the detection system. We also discuss plans for improving both the temporal resolution and the spatial resolution.},
  language  = {en}
}
@article{YangGuehrVecchioneetal.2016,
  author    = {Yang, Jie and G{\"u}hr, Markus and Vecchione, Theodore and Robinson, Matthew Scott and Li, Renkai and Hartmann, Nick and Shen, Xiaozhe and Coffee, Ryan and Corbett, Jeff and Fry, Alan and Gaffney, Kelly and Gorkhover, Tais and Hast, Carsten and Jobe, Keith and Makasyuk, Igor and Reid, Alexander and Robinson, Joseph and Vetter, Sharon and Wang, Fenglin and Weathersby, Stephen and Yoneda, Charles and Wang, Xijie and Centurion, Martin},
  title     = {Femtosecond gas phase electron diffraction with MeV electrons},
  series = {Faraday discussions},
  volume    = {194},
  journal   = {Faraday discussions},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {1359-6640},
  doi       = {10.1039/c6fd00071a},
  pages     = {563 -- 581},
  year      = {2016},
  abstract  = {We present results on ultrafast gas electron diffraction (UGED) experiments with femtosecond resolution using the MeV electron gun at SLAC National Accelerator Laboratory. UGED is a promising method to investigate molecular dynamics in the gas phase because electron pulses can probe the structure with a high spatial resolution. Until recently, however, it was not possible for UGED to reach the relevant timescale for the motion of the nuclei during a molecular reaction. Using MeV electron pulses has allowed us to overcome the main challenges in reaching femtosecond resolution, namely delivering short electron pulses on a gas target, overcoming the effect of velocity mismatch between pump laser pulses and the probe electron pulses, and maintaining a low timing jitter. At electron kinetic energies above 3 MeV, the velocity mismatch between laser and electron pulses becomes negligible. The relativistic electrons are also less susceptible to temporal broadening due to the Coulomb force. One of the challenges of diffraction with relativistic electrons is that the small de Broglie wavelength results in very small diffraction angles. In this paper we describe the new setup and its characterization, including capturing static diffraction patterns of molecules in the gas phase, finding time-zero with sub-picosecond accuracy and first time-resolved diffraction experiments. The new device can achieve a temporal resolution of 100 fs root-mean-square, and sub-angstrom spatial resolution. The collimation of the beam is sufficient to measure the diffraction pattern, and the transverse coherence is on the order of 2 nm. Currently, the temporal resolution is limited both by the pulse duration of the electron pulse on target and by the timing jitter, while the spatial resolution is limited by the average electron beam current and the signal-to-noise ratio of the detection system. We also discuss plans for improving both the temporal resolution and the spatial resolution.},
  language  = {en}
}