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(a) Principle of streaked diffraction: t0 is chosen such that section b of the long electron pulse passes through unpumped sample while section a of the pulse records the temporal evolution of the sample's structure after it has been pumped. (b) These slices of the probe pulse are afterwards spatially separated via a photo-triggered streak camera on to the detector screen.
Scanned and streaked diffraction patterns: (a) diffraction pattern of 4Hb -TaSe2 with the streak camera voltage switched off. The layered hexagonal crystal structure results in hexagonally arranged, bright Bragg diffraction peaks. The CDW supermodulation results in the appearance of six weak satellite reflections surrounding each Bragg reflection, referred to as CDW reflections. Panel (b) shows the streaked diffraction pattern.
Panel (a) shows the averaged streak of all available Bragg peaks. The much weaker CDW streaks are not visible due to the intensity scaling of the image. With an adjusted intensity scaling one of the six CDW streaks is displayed in panel (b) with panel (c) indicating the CDW streak with the pump beam on, t0 is clearly visible. Panel (d) shows the pumped and unpumped images subtracted from each other.
Comparison of transients obtained by streaking (data acquisition time 60 min, fluence of ) and scanning methods (data acquisition time 70 min, fluence of ). Although the streak length was ps, only 4 ps are plotted for direct comparison. The streak data were binned with a 100 interval, i.e., 3 data points were averaged, for better comparability to the scanned data. The fit model (solid lines) is briefly outlined in the text and elaborated in Ref. 8 .
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