Gating Pulse Synthesis

The visible pulse (gating pulse) enters the microscope, and together with the ultrafast electron pulses illuminate the nanostructure specimen (gold nanoparticle). The visible laser pulse kept at low power (~1.8 mJ/cm2) to avoid saturation. At the spatiotemporal overlapping, the coupling between the visible and electron pulses takes place. The signature of this coupling can be revealed by measuring the electron energy spectrum using the electron energy spectrometer attached to the microscope. The measured electron spectrum is shown in blue line curve in Fig. 2A. The white reddish part of the spectrum represents the ZLP while the shaded blue part shows the gated electron spectrum.
The temporal profile of the “original” ultrafast electron pulse
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2 A &B) due to the long pulse duration of the original electron pulses (~500 fs) respect to the gating window (~30fs). Therefore, we will use the same principle of the electron-photon coupling cross-correlation measurement to temporally characterize the gated electron pulse as explained earlier, utilizing another laser (NIR) pulse. The principle of this experiment is illustrated in Fig. 3A, which can be explained as follows; the gating optical pulse will maintain at τ_Vis=0fs to generate the gated electron pulse. The gated electrons are coupled with another laser pulse (NIR pulse (~1.4 mJ/cm2)). The gated electron pulse temporal profile can be retrieved from the coupling cross-correlation temporal profile between the gated electron pulse and the NIR pulse given the fact the pulse duration of the NIR pulse is …show more content…
4A and the coupling electron energy outline spectrum at τ_OAP=0 fs is shown in Fig. 4B. The ZLP has been subtracted from both the spectrogram and the outline spectrum for better visualization of the coupling peaks. The gating time window emulates the attosecond optical gating pulse which permits the generation of subfemtosecond electron pulse. The ratio of the number of attosecond-gated electrons respect to the total number of electrons of the original electron pulse represent the attosecond optical gating efficiency which depends on the original electron pulse duration. It is calculated by dividing the integration of the coupling part of the spectrum by the integration of all spectrum. This relation is illustrated in Fig. 4D. Thus, the attosecond optical gating of short (few tens femtosecond) electron pulse will allow the generation of the attosecond electron pulses with the sufficient strength to capture the electron motion in the act, which opens the way for attaining the attosecond resolution in electron microscopy and establishing the

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