Generation of sub-100 fs electron pulses for time-resolved electron diffraction using a direct synchronization method

Abstract

To investigate photoinduced phenomena in various materials and molecules, ultrashort pulsed x-ray and electron sources with high brightness and high repetition rates are required. The x-ray and electron’s typical and de Broglie wavelengths are shorter than lattice constants of materials and molecules. Therefore, photoinduced structural dynamics on the femtosecond to picosecond timescales can be directly observed in a diffraction manner by using these pulses. This research created a tabletop ultrashort pulsed electron diffraction setup that used a femtosecond laser and electron pulse compression cavity that was directly synchronized to the microwave master oscillator (∼3 GHz). A compressed electron pulse with a 1 kHz repetition rate contained 228 000 electrons. The electron pulse duration was estimated to be less than 100 fs at the sample position by using photoinduced immediate lattice changes in an ultrathin silicon film (50 nm). The newly developed time-resolved electron diffraction setup has a pulse duration that is comparable to femtosecond laser pulse widths (35–100 fs). The pulse duration, in particular, fits within the timescale of photoinduced phenomena in quantum materials. Our developed ultrafast time-resolved electron diffraction setup with a sub-100 fs temporal resolution would be a powerful tool in material science with a combination of optical pump–probe, time-resolved photoemission spectroscopic, and pulsed x-ray measurements.

Development of a Multitimescale Time-Resolved Electron Diffraction Setup: Photoinduced Dynamics of Oxygen Radicals on Graphene Oxide

“…Notably, the duration of the nanosecond laser and the jitter generated by the femtosecond and nanosecond lasers made it challenging to measure the structural dynamics at approximately 1−10 ns in the present setup. Further development of the multitimescale time-resolved electron diffraction setup with a jitter-free subnanosecond laser and a femtosecond laser with a cavity-lock loop 57 is expected to more seamlessly connect the dynamics on the femto-topicosecond and nano-to-millisecond timescales.…”

Streaking of a Picosecond Electron Pulse with a Weak Terahertz Pulse

“…We cannot generate a shorter electron pulse in this setup due to the geometry of the electron source. However, we have developed ultrafast time-resolved electron diffraction setups at 75 ,, and 100 keV accelerations with a radio frequency compression cavity. These two setups provide an electron pulse duration of ∼1 ps or <100 fs.…”

“…Thus, the characterization of the probe electron pulse is essential. The interactions of electric fields and electrons have been used to measure the duration of electron pulses, that is, the interactions of laser-plasma with electron pulses (plasma method), − the interactions of ponderomotive forces with electron pulses (ponderomotive method), − the interactions of the instantaneous high voltage electric fields and electron pulses (photoswitch streaking method), − and the interactions of electric fields generated by terahertz (THz) waves and electron pulses (THz streaking method). − The fast response form sample is also used to estimate the pulse duration. − The plasma method constructs a relatively simple setup compared with other methods; however, the accuracy of the pulse duration is limited since the laser plasma occurs on the picosecond time scale. The ponderomotive method requires a specific optical setup inside the vacuum chamber.…”