The microscopy system enables ultrafast electron microscopy without the need for an amplified femtosecond laser to generate electron pulses by photoemission. In addition, the microscopy system allows fast switching between pulsed operation and conventional continuous operation.
The microscopy system is based on a deflection cavity to chop the continuous beam from a conventional high-brightness electron gun into ultrashort electron pulses. The beam can be chopped either at 3 GHz rep rate using a deflection cavity in single mode or at 75 MHz rep rate using a deflection cavity in dual mode. To enable pump-probe experiments, the phase of the oscillating microwave fields in the deflection cavity has to synchronized to the femtosecond pump laser using the synchronizer system.
The deflection cavity is part of an insert on a vacuum flange, allowing it to be mounted into the extended column of a Thermo Fisher Scientific TEM. The deflection cavity is temperature controlled with 1 mK stability by water cooling and the construction of the insert mimimizes mechanical vibrations of the deflection cavity. By having a cross over in the deflection cavity the growth of the emittance due to chopping is mimimized so that the peak brightness is conserved. The energy spread of the beam is also minimally affected. Therefore the spatial resolution of the TEM is the same in pulsed mode and conventional continuous mode.
The microscopy system also allows low-dose-rate TEM operation in a very controlled way, which can be beneficial for mitigating radiation damage of sensitive samples.