Single-shot determination of focused FEL wave fields using iterative phase retrieval

Area of Science:

• Physics
• Optics
• Materials Science

Background:

• Accurate characterization of focused pulses is crucial for experiments at Self-Amplified-Spontaneous-Emission (SASE) Free-Electron-Lasers (FELs).
• Applications include imaging single non-crystalline biological particles, demanding precise focus property measurements.
• Existing methods like Hartmann wavefront sensors have limitations in comprehensive characterization.

Purpose of the Study:

• To develop and validate a novel diffractive imaging technique for full characterization of focused, single-shot FEL pulses.
• To provide a convenient and comprehensive method for measuring pulse wave fields and source-point variations.
• To benchmark the new technique against established methods, such as Hartmann wavefront sensing.

Main Methods:

• Utilized a diffractive imaging technique combined with an iterative phase retrieval algorithm.
• Performed theoretical calculations and experimental validation of the proposed method.
• Compared the technique's performance against a Hartmann wavefront sensor.

Main Results:

• The diffractive imaging technique successfully characterized highly focused, single-shot pulses.
• Both theoretical and experimental results confirmed the technique's effectiveness.
• The method provided comprehensive, shot-to-shot measurements of focused-pulse wave fields and source-point variations.

Conclusions:

• The developed diffractive imaging technique offers a powerful and convenient tool for FEL pulse characterization.
• It eliminates the need for manipulative optics between the focus and detector.
• This advancement is vital for improving precision in FEL-based experiments, particularly in biological imaging.