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Item type:Publication, Access status: with files , Data-model-guided framework for systemic emittance minimization in high brightness photoinjectors(American Physical Society (APS), 2026-05-08); ; ; ; Bunch shaping in electron linear accelerators is of critical importance, as it enables the realization of prescribed projection profiles along specific coordinates of the bunch distribution for linac-based x-ray free-electron laser (XFEL) applications. It is evident that temporally flattop electron bunches yield more uniform slice properties, reduced emittance growth, and enhanced FEL gain compared to conventional Gaussian profiles. In this work, we present a data- and model-guided framework that consists of a physics-informed model and an inverse emittance model for minimizing the bunch emittance through laser pulse shaping and the control of laser and accelerator parameters in high-brightness photoinjectors. With a temporal flattop laser shape selected, a flat slice emittance distribution along the bunch has been experimentally obtained at the European XFEL. A measured central slice emittance of about 0.4 μm at 250 pC is achieved using a 20 ps flattop laser pulse at the photocathode. Here we present the results of a commissioning experiment, marking a practical application of temporally flattop-shaped electron bunches for stable photon delivery in a user experiment week at the facility. Within limited tuning time, a pulse energy of 1.7 mJ has been achieved at photon energies of 7.1 and 7.6 keV for the two hard x-ray undulator beamlines, surpassing the user requirements. Such a data- and model-driven framework opens up new opportunities for end-to-end optimization of machine parameters, thereby enhancing the capabilities of large-scale FEL facilities.Publicationtype: Journal Article40 26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Novel photoinjector laser providing advanced pulse shaping for FLASH and EuXFELWe recently commissioned the Next GenerAtion Photocathode Laser system (NEPAL) in Hamburg’s XFEL facilities (FLASH and EuXFEL) and at DESY’s Photoinjector Test Facility (PITZ). The system delivers deep UV pulse trains up to 1 ms long at repetition rates as high as 4.5 MHz, with temporal and spatial shaping capabilities and individual amplitude control for bunch charge manipulation. The shaping features enable the generation of exceptionally low emittance electron beams, essential for extending the EuXFEL X-ray photon energy beyond 25 keV and for future high duty cycle upgrades. Temporal shaping is achieved through a high-resolution spatial light modulator in the near-infrared driver laser, allowing precise spectral amplitude and phase control of UV pulses. We will present advanced control schemes that pre-compensate for laser nonlinearities and initial experimental results at EuXFEL. We generated UV flat-top pulse profiles with durations ranging from 10ps to 20ps and successfully transferred them onto the electron beam. This achievement represents a significant step toward emittance optimization at EuXFEL and will expand the facility's operational energy range in the near future.Publicationtype: Conference Paper32 26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Temporal shaping of UV picosecond pulses for photoinjectors(2025); ; 22