THz streak camera method for synchronous arrival time measurement of two-color hard X-ray FEL pulses.

The two-color operation of free electron laser (FEL) facilities allows the delivery of two FEL pulses with different energies, which opens new possibilities for user experiments. Measuring the arrival time of both FEL pulses relative to the external experimental laser and to each other improves the temporal resolution of the experiments using the two-color FEL beam and helps to monitor the performance of the machine itself. This work reports on the first simultaneous measurement of the arrival times of two hard X-ray FEL pulses with the THz streak camera. Measuring the arrival time of the two FEL pulses, the relative delay between them was calculated and compared to the set values. Furthermore, we present the first comparison of the THz streak camera method to the method of FEL induced transient transmission. The results indicate a good agreement between the two methods.