Abstract
Streaking of photoelectrons with optical lasers has been widely used for temporal characterization of attosecond extreme ultraviolet pulses. Recently, this technique has been adapted to characterize femtosecond x-ray pulses in free-electron lasers with the streaking imprinted by far-infrared and terahertz (THz) pulses. Here, we report successful implementation of THz streaking for time stamping of an ultrashort relativistic electron beam, whose energy is several orders of magnitude higher than photoelectrons. Such an ability is especially important for MeV ultrafast electron diffraction (UED) applications, where electron beams with a few femtosecond pulse width may be obtained with longitudinal compression, while the arrival time may fluctuate at a much larger timescale. Using this laser-driven THz streaking technique, the arrival time of an ultrashort electron beam with a 6-fs (rms) pulse width has been determined with 1.5-fs (rms) accuracy. Furthermore, we have proposed and demonstrated a noninvasive method for correction of the timing jitter with femtosecond accuracy through measurement of the compressed beam energy, which may allow one to advance UED towards a sub-10-fs frontier, far beyond the approximate 100-fs (rms) jitter.
- Received 19 January 2018
- Revised 15 April 2018
DOI:https://doi.org/10.1103/PhysRevX.8.021061
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
To deduce the atomic structure of a material or capture the rapid motion of atoms, researchers often use a “pump-probe” technique, in which a laser initiates the dynamics that are then probed by a pulse of x rays, electrons, or a second laser. When an electron bunch is used as the probe pulse, the temporal resolution depends primarily on the width of the electron pulse as well as variations in their arrival times. But when millions of electrons are crammed together, they repel one another, which broadens the pulse and reduces the details that the probe can reveal. We found a way to mark the arrival times of the electron beam, which improves the temporal resolution of pump-probe experiments by 2 orders of magnitude.
A dispersed pulse of electrons can be compressed with a radio-frequency buncher cavity, in which radio waves slow down electrons at the head of a pulse and accelerate electrons at the tail. However, the reduction in pulse width is typically achieved at the cost of increasing the arrival timing jitter. We time-stamped the arrival time of a relativistic electron beam using a terahertz pulse. The terahertz pulse and the electrons interact in a narrow slit, which deflects the electron beam. By correlating these deflections with the terahertz pulses, we can measure and sort the beam arrival time on a shot-by-shot basis, allowing us to record the pulse arrival time with an accuracy of about 1.5 fs.
With a more optimized setup, our technique may enable attosecond electron diffraction metrologies that are capable of capturing the ultrafast and ultrasmall processes in new regimes.
