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We report on the complete characterization of time resolution in an ultrafast electron diffraction (UED) instrument based on radio-frequency electron pulse compression. The temporal impulse response function of the instrument was determined directly in pump-probe geometry by performing electron-laser pulse cross-correlation measurements using the ponderomotive interaction. With optimal settings, a stable impulse response of 334±10 fs was measured at a bunch charge of 0.1 pC (6.24 × 105 electrons/pulse); a dramatic improvement compared to performance without pulse compression. Phase stability currently limits the impulse response of the UED diffractometer to the range of 334–500 fs, for bunch charges ranging between 0.1 and 0.6 pC.
Chatelain et al. (Mon,) studied this question.