Abstract
We demonstrate a noninvasive time-sorting method for ultrafast electron diffraction (UED) experiments with radio frequency (rf)-compressed electron beams. We show that electron beam energy and arrival time at the sample after the rf compression are strongly correlated, such that the arrival time jitter may be corrected through the measurement of the beam energy. The method requires minimal change to the infrastructure of most of the UED machines and is applicable to both keV and MeV UED. In our experiment with ∼3 MeV beam, the timing jitter after the rf compression is corrected with a 35-fs root mean square (rms) accuracy, limited by the energy stability. For keV UED with a high energy stability, sub-10 fs accuracy in time-sorting should be readily achievable. This time-sorting technique allows us to retrieve the 2.5 THz oscillation related to coherent A1g phonon in the laser-excited Bismuth film and extends the temporal resolution of UED to a regime far beyond the 100–200 fs rms jitter limitation.
Highlights
Ultrafast electron diffraction (UED) has emerged as a powerful tool with high temporal-spatial resolving power, providing direct insight into the structural dynamics of matter.1,2 In ultrafast electron diffraction (UED) experiments, the dynamics are initiated by an ultrashort pump laser and probed by a delayed electron pulse
We demonstrate a noninvasive time-sorting method for ultrafast electron diffraction (UED) experiments with radio frequency-compressed electron beams
We show that electron beam energy and arrival time at the sample after the rf compression are strongly correlated, such that the arrival time jitter may be corrected through the measurement of the beam energy
Summary
Ultrafast electron diffraction (UED) has emerged as a powerful tool with high temporal-spatial resolving power, providing direct insight into the structural dynamics of matter. In UED experiments, the dynamics are initiated by an ultrashort pump laser and probed by a delayed electron pulse. Because the detector has a central hole to allow the un-diffracted beam to pass through, it is straightforward to simultaneously measure both the diffraction pattern and beam arrival time with a downstream energy spectrometer This method has been used to retrieve the A1g phonon oscillation in laser-excited Bismuth. No oscillation has been observed in the raw data without the jitter correction This measure-and-sort method is applicable to both keV and MeV UED and can be used to correct both the short-term timing jitter and the long-term timing drift in the rf-compressed UED. The timing jitter of the rf-compressed beam is corrected with 35-fs rms accuracy, limited by the energy stability of the electron beam before the buncher. Since keV UED has high stability in beam energy, an accuracy of a few femtoseconds should be readily achievable with this time-sorting method
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