Ultrafast Electron Diffraction (UED) is an indispensable tool that enables the study of ultrafast dynamics on an atomic/molecular scale. Ultrashort high brightness electron beams are needed to capture the critical ultrafast events, particularly for studying the irreversible biochemical processes in the single-shot mode. However, the Coulomb interactions in the space-charge dominated electron beam limit attainable beam length and dilute beam quality during its propagation. The beam emittance increases significantly during propagation due to the severe space charge effect (SCE) because of low energy. It is essential to understand the emittance evolution behavior in detail during its passage for improving the UED performance further. The multi-slit method is selected to eliminate the SCE influence on the measurement by a low sampling rate of the electrons, making it possible to diagnose the emittance. However, the insufficient samplings create challenges in reconstructing the original beam information. This paper introduces an algorithm that can precisely reproduce beam parameters from severely under-sampled data.
The orientation of molecules is essential to study molecular angle-differential properties such as ionization and scattering cross-sections in material physics and chemistry. Ultrafast electron diffraction (UED) facilities offer effective ways to explore the ultrafast dynamics of orientated molecules. Generally, the orientation of molecules is generated by a strong dc-field. However, the presence of a strong field may influence detection outcome. Field-free orientation of molecules is preferable, avoiding the disadvantages of traditional dc-field excitation. This paper proposes a practical and versatile method for field-free molecular orientation using the co-rotating two-color circularly polarized ultrafast laser pulses, and the orientation of the molecules can be controlled by the relative phase of the two-color laser fields. We also performed our simulation in CO molecules with the Born-Oppenheimer and rigid rotor approximations, and the light-molecule interaction Hamiltonian is given by the low-order perturbation theory.
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