Crystallography

The crystallography system consists of the 100 keV DC electron gun, the laser incoupler, the 3 GHz compression cavity, two solenoid magnetic lenses for collimating and focusing the electron beam, the synchronizer and a temperature controller. Optionally, a 3 GHz deflection cavity on a translation stage can be added for pulse length diagnostics at the sample position.

The crystallography system enables single-shot electron diffraction at 100 keV beam energy. To realize this, a ~1 μJ femtosecond 266 nm laser pulse is directed via the laser Incoupler onto the cathode surface of the 100 keV DC electron gun. The generated 0.1-1 pC 100 keV electron bunch will expand rapidly in all directions due to Coulomb repulsion. The transverse expansion of the beam is stopped by the first solenoid, mounted directly on the exit of the 100 keV DC electron gun. To invert the longitudinal expansion the transversely collimated beam is sent through the compression cavity, which has its microwave phase locked to the femtosecond laser pulses using the synchronizer. For proper synchronization, the compression cavity has to be temperature controlled with a stability of 1 mK. The combination of the compression cavity and a second solenoid magnetic lens allows the beam to be both focused transversely and compressed longitudinally onto the sample. The overall length of the entire crystallography setup is approximately 1 m.

We can deliver a complete system with a conditioned 100 keV DC electron gun and a temperature stabilized compression cavity, which stays exactly on resonance and fully synchronized when full microwave power is fed in.