Tunable x-ray free electron laser multi-pulses with nanosecond separation

Area of Science:

• Atomic and Molecular Physics
• Materials Science
• Ultrafast Science

Background:

• X-ray Free Electron Lasers (XFELs) generate high-intensity, ultrashort X-ray pulses crucial for probing matter at ultrafast timescales.
• Current XFEL capabilities for pump-probe experiments are limited by short pulse delays ( < 1 picosecond) using single-bucket methods.
• This limitation hinders the investigation of slower dynamic processes in materials and molecules.

Purpose of the Study:

• To develop and demonstrate a novel method for extending the time delay between consecutive X-ray pulses from XFELs.
• To enable the study of longer time-scale dynamics in materials and chemical processes using X-ray pump-X-ray probe spectroscopy.

Main Methods:

• Implementation of a novel 'two-bucket' scheme for generating XFEL pulse pairs.
• Achieving controllable delays ranging from 350 picoseconds to hundreds of nanoseconds in discrete steps.
• Experimental validation of the two-bucket scheme at the Linac Coherent Light Source (LCLS-I) and LCLS-II hard X-ray undulators.

Main Results:

• Successfully demonstrated a two-bucket scheme capable of generating X-ray pulse pairs with delays from 350 picoseconds to hundreds of nanoseconds.
• The performance of individual pulses within the two-bucket scheme is comparable to single-pulse operation.
• Experimental verification confirmed the feasibility and effectiveness of the proposed method at leading XFEL facilities.

Conclusions:

• The novel two-bucket scheme significantly expands the accessible time delays for X-ray pump-X-ray probe experiments.
• This advancement opens new avenues for exploring slower dynamic phenomena in various scientific fields.
• The method is compatible with existing and next-generation XFEL infrastructure.