Partial-coherence method to model experimental free-electron laser pulse statistics.

Area of Science:

• Physics
• Optics
• Laser Science

Background:

• Free-electron lasers (FELs) operating in self-amplified spontaneous emission (SASE) mode produce complex temporal pulse shapes.
• Understanding these pulse shapes is crucial for advanced experiments, but theoretical modeling can be challenging.

Purpose of the Study:

• To develop a general numerical approach for modeling FEL temporal pulse shapes in the SASE mode.
• To generate pulse shape sets that satisfy statistical criteria predicted by FEL theory.
• To validate the numerical approach against experimental data from the Free-electron LASer at Hamburg (FLASH).

Main Methods:

• A random partial-coherence approach was employed for numerical calculations.
• Sets of temporal pulse shapes were generated based on statistical criteria.
• The calculated pulse characteristics were compared with experimental measurements from FLASH.

Main Results:

• The numerical approach successfully generated model sets of FEL temporal pulse shapes.
• The calculated pulse shapes satisfied statistical criteria consistent with FEL theory.
• The model accurately reproduced experimentally measured characteristics, including average spectrum, single-shot spectral shape, and pulse duration at FLASH.

Conclusions:

• The developed numerical method provides a convenient and accurate tool for analyzing and theoretically modeling FEL light.
• The approach's high-precision agreement with experimental data, without requiring detailed machine parameters, enhances its utility for nonlinear optical and pump-probe experiments.