Electron Bunch Timing with Femtosecond Precision in a Superconducting Free-Electron Laser

Abstract

High-gain free-electron lasers (FELs) are capable of generating femtosecond x-ray pulses with peak brilliances many orders of magnitude higher than at other existing x-ray sources. In order to fully exploit the opportunities offered by these femtosecond light pulses in time-resolved experiments, an unprecedented synchronization accuracy is required. In this Letter, we distributed the pulse train of a mode-locked fiber laser with femtosecond stability to different locations in the linear accelerator of the soft x-ray FEL FLASH. A novel electro-optic detection scheme was applied to measure the electron bunch arrival time with an as yet unrivaled precision of 6 fs (rms). With two beam-based feedback systems we succeeded in stabilizing both the arrival time and the electron bunch compression process within two magnetic chicanes, yielding a significant reduction of the FEL pulse energy jitter.

Ultrashort Free-Electron Laser X-ray Pulses

“…Another essential requirement for every ultrafast experiment that relies on a synchronized optical laser for pump or probe is precise information about the relative arrival time between the two lasers. Steady progress in this regard has been made [51,52,58,69,101,103,[117][118][119][120], as was demonstrated throughout this review, and electron acceleration designs relying on superconducting linear accelerators [19,20] open up even better prospects for temporal synchronization [121]. Nevertheless, a complete and direct single-shot measurement in the time domain that reports both the exact XFEL pulse temporal structure and arrival time simultaneously and which is applicable over a broad range of X-ray pulse durations remains elusive.…”

XFEL experiments: jitter of pump–probe time delays and pulse intensities

“…X-ray techniques, in particularly XFEL techniques have proven to be extremely efficient, but a number of difficulties still limit, for the time being, their intrinsic power: the shot-to shot dispersion of pump-probe time delays and of pulse intensities. An important efforts has been made to solve this problem experimentally [2] [3] [4][5] [6] [7][8] [9]. The recent measure and sort technique [10] merits attention in this context.…”

Single-shot pulse duration monitor for extreme ultraviolet and X-ray free-electron lasers

“…High-resolution pump-probe experiments require a precisely characterized FEL pulse and precise synchronization to an external optical pump-probe laser. While so far different schemes for arrival time measurements have been developed [11][12][13][14][15][16][17][18][19][20][21][22][23] , insufficient characterization of the XUV or X-ray FEL pulse duration at the experimental station remains the main handicap of single pass free-electron lasers that rely on self-amplified spontaneous emission (SASE).…”

“…Direct and indirect techniques for XUV and X-ray pulse duration measurement [22][23][24][25][26][27][28][29][30][31][32] and pulse arrival time monitoring [11][12][13][14][15][16][17][18][19][20][21][22][23] are subjects of active research and most are already implemented in the FEL machine environment. In particular for XUV pulses, the experiments must be realized under vacuum conditions.…”

“…In the case of timing diagnostic tools, a disadvantage of many methods is that the spatial distance to the actual experiment introduces an additional timing uncertainty. One category of diagnostics is designed only to measure the arrival time of the electron bunches with respect to the pump-probe laser [11][12][13] . This has the disadvantage that the path length drift of the photon beamlines is omitted.…”