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High-power, short-pulse laser-driven fast electrons can rapidly heat and ionize a high-density target before it hydrodynamically expands. The transport of such electrons within a solid target has been studied using two-dimensional (2D) imaging of electron-induced Kα radiation. However, it is currently limited to no or picosecond scale temporal resolutions. Here, we demonstrate femtosecond time-resolved 2D imaging of fast electron transport in a solid copper foil using the SACLA x-ray free electron laser (XFEL). An unfocused collimated x-ray beam produced transmission images with sub-micron and ∼10 fs resolutions. The XFEL beam, tuned to its photon energy slightly above the Cu K-edge, enabled 2D imaging of transmission changes induced by electron isochoric heating. Time-resolved measurements obtained by varying the time delay between the x-ray probe and the optical laser show that the signature of the electron-heated region expands at ∼25% of the speed of light in a picosecond duration. Time-integrated Cu Kα images support the electron energy and propagation distance observed with the transmission imaging. The x-ray near-edge transmission imaging with a tunable XFEL beam could be broadly applicable for imaging isochorically heated targets by laser-driven relativistic electrons, energetic protons, or an intense x-ray beam.
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Non-invasive low charge electron beam time-of-arrival diagnostic using a plasmonics-enhanced photoconductive antenna
The use of a plasmonics-enhanced photoconductive antenna (PCA) optically gated by a near infrared (NIR) pulse enables non-invasive time-of-arrival measurements of a low charge electron beam with respect to the NIR reference, achieving picosecond resolution. The measured signal values show the expected scaling with the beam charge and distance from PCA to the beam axis, as the PCA samples the electric field of the passing electron beam. We operate the device with an NIR spot size much larger than the PCA active-area, resulting in a very simple optical setup and alignment procedure, making the plasmonics-enhanced PCA a preferred alternative to more complex timing diagnostics for applications requiring non-invasive picosecond or sub-picosecond timestamping.
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- Award ID(s):
- 1734215
- PAR ID:
- 10595043
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- Applied Physics Letters
- Volume:
- 113
- Issue:
- 19
- ISSN:
- 0003-6951
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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