Speaker
Description
The recently installed NEPAL photocathode lasers at FLASH, PITZ and the European XFEL, deliver exceptional stability, reliability, and flexibility for XFEL operation. Their programmable spectral filter enables precise control of intensity and phase of the near-infrared seed-laser pulses which are then nonlinearly amplified and wavelength converted to UV. We developed an adaptive pulse-shaping method to use the filter for UV output temporal profile control (target: flat-top, triangular, inverted parabola or Gaussian). We utilize a differentiable physics model of the laser system which includes all nonlinearities. We iterate between refining the physics model parameters to match real-system measurements (model fitting) and refining the spectral filter parameters for temporal profile optimization (control optimization). We typically reach convergence in 50 iteration pairs.
We applied this tool to match the temporal laser pulse profiles of the two NEPAL systems at the European XFEL, leading to identical SASE X-ray output without any accelerator retuning. A recent study at the photoinjector test stand PITZ showed significant emittance dependence on laser pulse duration and shape with the potential to enhance EuXFEL performance in the near future.
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