A scheme for a shot-to-shot, femtosecond-resolved pulse length and arrival time measurement of free electron laser x-ray pulses that overcomes the time jitter problem between the FEL and the laser

Abstract

The recent entry of X-ray free electron lasers (FELs) to all fields of physics has created an enormous need, both from scientists and operators, for better characterizationof the beam created by these facilities. Of particular interest is the measurement of the arrival time of the FEL pulse relative to a laser pump, for pump-probe experiments, andthe measurement of the FEL pulse length. This article describes a scheme that corrects one of the major sources of uncertainty in these types of measurements, namelythe jitter in the arrival time of the FEL relative to an experimental laser beam. The setup presented here uses a combination of THz streak cameras and a spectral encoding setup to reduce theeffect of an FEL's jitter, leaving the pulse length as the only variable that can affect the accuracy of the pulse length and arrival time measurement. A discussion of underlyingprinciples is also provided.