Chirped seeded free-electron lasers: self-standing light sources for two-color pump-probe experiments

Area of Science:

• Atomic, Molecular, and Chemical Physics
• Optics
• Condensed Matter Physics

Background:

• Pump-probe spectroscopy is a powerful technique for studying ultrafast dynamics.
• Free electron lasers (FELs) offer tunable, high-intensity radiation for advanced experiments.
• Generating multiple, controlled pulses from FELs is crucial for complex spectroscopic studies.

Purpose of the Study:

• To demonstrate a dynamical regime in single-pass free electron lasers (FELs).
• To enable two-color pump-probe experiments in the vacuum ultraviolet (VUV) and X-ray domains.
• To utilize FEL emission as both the pump and the probe in these experiments.

Main Methods:

• Inducing the FEL process by triggering with a powerful laser pulse.
• Imparting a significant and adjustable frequency chirp to the triggering laser pulse.
• Experimental validation on the FERMI@Elettra free-electron laser facility.

Main Results:

• The output FEL radiation splits into two pulses with different central wavelengths and temporal separation.
• Independent control over both spectral and temporal distances between the generated FEL pulses.
• Theoretical description of the phenomenon shows good agreement with experimental observations.

Conclusions:

• The demonstrated dynamical FEL regime facilitates advanced two-color pump-probe experiments.
• This technique provides a novel method for generating controlled, dual-wavelength FEL pulses.
• The findings pave the way for new investigations in VUV and X-ray spectroscopy.