Abstract
In this paper we study a new geometry setup for electro-optic sampling (EOS) where the electron beam runs parallel to the $⟨110⟩$ face of a ZnTe crystal and the probe laser is perpendicular to it and to the beam path. The simple setup is used to encode the time-of-arrival information of a $3.5\text{ }\text{ }\mathrm{MeV}l10\text{ }\text{ }\mathrm{pC}$ electron bunch on the spatial profile of the laser pulse. The electric field lines inside the dielectric bend at an angle due to a relatively large ($n\ensuremath{\sim}3$) index of refraction of the ZnTe crystal. We found theoretically and experimentally that the EOS signal can be maximized with a proper choice of incoming laser polarization angle. We achieved single-shot nondestructive measurement of the relative time of arrival between the pump and the probe beams thus improving the temporal resolution of ultrafast relativistic electron diffraction experiments.
Highlights
Electro-optic sampling (EOS) based temporal diagnostics of relativistic electron beams has been a very active field in the past decade
Favored by the spread of ultrafast laser techniques to the particle accelerator field, sub-ps relativistic electron beams are becoming increasingly common with applications in high gain free-electron lasers [1], in the context of laser based advanced accelerators [2], and more recently in direct structural dynamics measurements as ultrafast diffraction probes [3,4]
The application of EOS to the TOA measurement is very important for pump-probe experiments that require determining exactly how long after the laser excitation the probe beam captures the structure of the sample under study
Summary
Electro-optic sampling (EOS) based temporal diagnostics of relativistic electron beams has been a very active field in the past decade. At the UCLA Pegasus laboratory we have shown that, by increasing the beam energy to 3.5 MeV, we can generate electron beams with rms bunch lengths of few hundred fs and with up to 3 orders of magnitude more particles than currently available with nonrelativistic sources These ultrashort electron pulses are suitable to obtain single-shot diffraction patterns as shown, opening new possibilities in the study of ultrafast dynamics at the atomic scale. In order to fully take advantage of the intense ultrashort probe beams generated by the rf photoinjector, one has to solve the difficult problem of minimizing the jitter in the time of arrival, or obtain a nondestructive TOA measurement and postprocess the images using this information The latter approach is discussed in this paper. Three mirrors are introduced as a delay so that the path lengths from the beam splitter to the EOS interaction point and from the beam splitter to the diffraction target are equal, accounting for the time that the electron beam takes to travel from one to the other (see Fig. 2)
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