Superradiant cascade in a seeded free-electron laser.

Area of Science:

• Physics
• Quantum Optics
• Laser Science

Background:

• Free-electron lasers (FELs) are powerful sources of tunable radiation.
• Superradiance is an enhanced spontaneous emission phenomenon.
• Cascaded FEL schemes offer potential for advanced light generation.

Purpose of the Study:

• To demonstrate the concept of the free-electron laser (FEL) superradiant cascade.
• To generate radiation at a shorter wavelength (200 nm) using a cascaded FEL scheme.
• To validate experimental findings with particle simulations.

Main Methods:

• Utilized a cascaded FEL scheme with distinct modulator and radiator undulator sections.
• Employed a short, intense seed laser pulse (400 nm).
• Conducted detailed spectral and intensity measurements of the generated radiation.
• Performed numerical particle simulations using the FEL code GENESIS 1.3.

Main Results:

• Successfully generated 200 nm radiation, the second harmonic of the seed pulse.
• Confirmed superradiance of the ultrashort pulse through spectral structure and intensity measurements.
• Observed energy growth trends along the undulator consistent with superradiant cascade.
• Achieved satisfactory agreement between experimental results and GENESIS 1.3 simulations.

Conclusions:

• The free-electron laser (FEL) superradiant cascade is a viable concept for generating high-intensity, short-wavelength radiation.
• Cascaded FEL schemes provide a pathway for efficient harmonic generation and pulse manipulation.
• Numerical simulations are a reliable tool for predicting and understanding FEL performance.