Speaker
Description
Small-scale accelerator-based radiation sources have been used for developing advanced technologies and exploring new science with high convenience and low cost. We have developed a 3 MeV ultrafast electron diffraction (UED) probe technology that nominally reduces the electron bunch duration and the arrival time jitter to the sub-femtosecond level. This simple configuration uses a radiofrequency photogun and a 90° achromatic bend and is designed to provide effectively jitter-free conditions. THz streaking measurements reveal an electron bunch duration of 25 fs, even for a charge as high as 0.6 pC, and an arrival time jitter of 7.8 fs, the latter limited only by the measurement accuracy. From pump-probe measurements of photoexcited bismuth films, the instrument response function was determined to 31 fs. Recently, we proposed a simple way to further compress the electron bunch duration to sub-10 fs based on installing an energy filter in the dispersion section of the achromatic bend. Through numerical simulations, we demonstrate that the electron bunches can be compressed, at the sample position, to a 6.2 fs duration for a 100 fC charge. This result suggests that the energy filtering approach is more viable and effective than complicated beam-shaping techniques that commonly handle the nonlinear distribution of the electron beam.
In an attempt to design smaller THz free-electron laser (FEL) devices capable of producing higher output powers in the THz spectral region of 1-2 THz, we have developed a microtron accelerator that can accelerate electron beams from 3-6 MeV, with a measured macropulse current of more than 40 mA. The new THz FELs use hybrid electromagnetic (EM) undulators that are two to four times shorter in length than the previous 2-m-long undulator and waveguide resonators with mode cross-sectional areas that are more than two times smaller than the parallel-plate waveguide in the existing FEL. We confirm that the gains and losses of the more compact FELs are sufficient for lasing, and we estimate that an average output power of approximately 1 W is possible with an efficiency approximately 10 times greater than the existing FEL. The minimum size of the THz FEL system, including a high-voltage pulse modulator, is estimated to be approximately 1.5 m × 2.0 m.
