IT-8-P-6102 Development of femtosecond time-resolved relativistic-energy electron microscopy

The direct visualization of structural dynamic processes in matter occurring on femtosecond time scales over sub-nanometer (even atomic) spatial dimensions has long been a goal in scientists. Transmission electron microscopy (TEM) is a powerful tool to observe directly the image from specimen with high spatial resolution. When coupled with time resolution, it, which also called ultrafast electron microscopy (UEM), would be the strongest tool for the study of ultrafast dynamics in materials. Currently, the UEM with the time-spatial resolution of nanosecond and nanometer has been achieved in conventional TEM through the use of photo-activated electron source driven by a nanosecond laser in the non-space-charge-limited regime with ns-long pulse length. A large number of important phenomena, i.e. phase transformations, melting, resolidification, nucleation and growth of damage in nanosecond time region, have been investigated. To achieve a high time resolution overcoming the space-charge limitation, we have proposed and designed a femtosecond time-resolved relativistic-energy electron microscopy using a photocathode radio-frequency (RF) electron gun. In 2009, we have developed a new RF gun to generate a low-emittance femtosecond-bunch electron beam: 100 fs and 0.2 mm-mrad, which are essential for the achievement of nm-fs space-time resolution in future. In 2010, we constructed successfully an instrument of ultrafast relativistic-energy electron diffraction (UED) using the RF gun. The time resolution of 100 fs has been achieved. A first prototype of RF gun based relativistic-energy TEM has been constructed at Osaka University in 2012. Both the static measurements of both relativistic-energy electron diffraction and image have been succeeded in the prototype. In this poster, the activities on UED and UEM are introduced. The requirements and limitations of the beam parameters in UEM are reviewed. The concept and design of RF gun based relativistic-energy TEM prototype are reported. The beam dynamics and challenges in femtosecond RF gun will be discussed. Finally, some demonstrations of the relativistic-energy TEM images, the single-shot and time-resolved UED measurements are reported.