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| Auteurs principaux: | , , |
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| Format: | Preprint |
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2024
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| Accès en ligne: | https://arxiv.org/abs/2406.13614 |
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| _version_ | 1866909324304973824 |
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| author | Chen, Jialiang Willis, Simon A. Flannigan, David J. |
| author_facet | Chen, Jialiang Willis, Simon A. Flannigan, David J. |
| contents | Efforts to push the spatiotemporal imaging-resolution limits of femtosecond (fs) laser-driven ultrafast electron microscopes (UEMs) to the combined angstrom-fs range will benefit from stable sources capable of generating high bunch charges. Recent demonstration of unconventional off-axis photoemitting geometries are promising, but connections to the observed onset of structural dynamics are yet to be established. Here we use the in-situ photoexcitation of coherent phonons to quantify the relative time-of-flight (r-TOF) of photoelectron packets generated from the Ni Wehnelt aperture and from a Ta cathode set-back from the aperture plane. We further support the UEM experiments with particle-tracing simulations of the precise electron-gun architecture and photoemitting geometries. In this way, we measure discernable shifts in electron-packet TOF of tens of picoseconds for the two photoemitting surfaces. These shifts arise from the impact the Wehnelt-aperture off-axis orientation has on the electron-momentum distribution, which modifies both the collection efficiency and the temporal-packet distribution relative to on-axis emission. Future needs are identified; we expect this and other developments in UEM electron-gun configuration to expand the range of materials phenomena that can be directly imaged on scales commensurate with fundamental structural dynamics. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2406_13614 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Relative Time-of-Flight Measurement in an Ultrafast Electron Microscope Chen, Jialiang Willis, Simon A. Flannigan, David J. Materials Science Efforts to push the spatiotemporal imaging-resolution limits of femtosecond (fs) laser-driven ultrafast electron microscopes (UEMs) to the combined angstrom-fs range will benefit from stable sources capable of generating high bunch charges. Recent demonstration of unconventional off-axis photoemitting geometries are promising, but connections to the observed onset of structural dynamics are yet to be established. Here we use the in-situ photoexcitation of coherent phonons to quantify the relative time-of-flight (r-TOF) of photoelectron packets generated from the Ni Wehnelt aperture and from a Ta cathode set-back from the aperture plane. We further support the UEM experiments with particle-tracing simulations of the precise electron-gun architecture and photoemitting geometries. In this way, we measure discernable shifts in electron-packet TOF of tens of picoseconds for the two photoemitting surfaces. These shifts arise from the impact the Wehnelt-aperture off-axis orientation has on the electron-momentum distribution, which modifies both the collection efficiency and the temporal-packet distribution relative to on-axis emission. Future needs are identified; we expect this and other developments in UEM electron-gun configuration to expand the range of materials phenomena that can be directly imaged on scales commensurate with fundamental structural dynamics. |
| title | Relative Time-of-Flight Measurement in an Ultrafast Electron Microscope |
| topic | Materials Science |
| url | https://arxiv.org/abs/2406.13614 |