Self-enhanced coherent harmonic amplification in seeded free-electron lasers

Area of Science:

• Physics
• Materials Science
• Spectroscopy

Background:

• High-intensity, ultrashort, fully coherent X-ray pulses are crucial for advanced spectroscopic techniques.
• Existing methods face limitations in brightness and coherence for soft X-ray generation.

Purpose of the Study:

• To propose and validate a novel scheme for generating high-brightness, femtosecond-scale soft X-ray radiation.
• To achieve MHz repetition rates for soft X-ray generation using a seeded free-electron laser (FEL).

Main Methods:

• Utilized principles of self-modulation and superradiance in a seeded free-electron laser (FEL).
• Employed three-dimensional simulations based on the Shanghai soft X-ray FEL facility parameters.
• Investigated amplification of weak energy modulation in pre-bunched electron beams.

Main Results:

• Demonstrated generation of ultrashort coherent radiation pulses (around 2 GW) in the water window spectral range.
• Achieved coherent signals up to the 15th harmonic of a 266-nm seed laser.
• Confirmed feasibility with electron beam energy modulation as low as 2.3 times the slice energy spread.

Conclusions:

• The proposed scheme effectively generates ultrashort, coherent soft X-ray pulses at MHz repetition rates.
• This advancement promises to significantly enhance capabilities in X-ray spectroscopy and related fields.
• Self-enhanced coherent energy modulation is key to producing high-harmonic coherent signals.