Correlation of refractive index based and THz streaking arrival time tools for a hard X-ray free-electron laser.

To fully exploit ultra-short X-ray pulse durations routinely available at X-ray free-electron lasers to follow out-of-equilibrium dynamics, inherent arrival time fluctuations of the X-ray pulse with an external perturbing laser pulse need to be measured. In this work, two methods of arrival time measurement were compared to measure the arrival time jitter of hard X-ray pulses. The methods were photoelectron streaking by a THz field and a transient refractive index change of a semiconductor.

Arrival time fluctuation of the SwissFEL photocathode laser: characterization by a single color balanced cross correlator.

The arrival time jitter and drift of the photocathode drive laser has an important impact on the performance of a Free-Electron-Laser (FEL). It adversely affects the beam energy jitter, bunch length jitter and bunch arrival time jitter, which becomes especially important for pump-probe experiments with femtosecond time resolution. To measure both parameters background free and stabilize the drift of the Yb:CaF based laser we use a well designed balanced optical cross correlator.

Optical second harmonic generation in LiBO modulated by intense femtosecond X-ray pulses.

Many of the scientific applications for X-ray free-electron lasers seek to exploit the ultrashort pulse durations of intense X-rays to obtain femtosecond time resolution of various processes in a "pump-probe" scheme. One of the limiting factors for such experiments is the timing jitter between the X-rays and ultrashort pulses from more conventional lasers operating at near-optical wavelengths. In this work, we investigate the potential of using X-ray-induced changes in the optical second harmonic generation efficiency of a nonlinear crystal to retrieve single-shot arrival times of X-ray pulses with respect to optical laser pulses.

Femtosecond resolution timing jitter correction on a TW scale Ti:sapphire laser system for FEL pump-probe experiments.

Intense ultrashort pulse lasers are used for fs resolution pump-probe experiments more and more at large scale facilities, such as free electron lasers (FEL). Measurement of the arrival time of the laser pulses and stabilization to the machine or other sub-systems on the target, is crucial for high time-resolution measurements. In this work we report on a single shot, spectrally resolved, non-collinear cross-correlator with sub-fs resolution.

Improving coherent contrast of petawatt laser pulses.

We report on an experimental study of the "coherent" contrast feature that frequently appears in petawatt(PW)-class laser pulses as an exponentially-rising pedestal within a few tens of picoseconds of the compressed pulse. We show that scattering from the diffraction gratings in the stretcher is the principal source of this feature. Replacing the gratings by new, higher-quality components resulted in an order-of-magnitude reduction in the intensity of the pedestal.