A non-invasive online photoionization spectrometer for FLASH2

Area of Science:

• Atomic, Molecular, and Optical Physics
• Plasma Physics
• Accelerator Physics

Background:

• Self-amplified spontaneous emission (SASE) free-electron lasers (FELs) exhibit stochastic behavior, leading to pulse-to-pulse variations in radiation properties like photon energy.
• These fluctuations significantly impact photon-matter interaction studies, necessitating precise, real-time feedback for each photon bunch to interpret experimental data accurately.
• Existing monitoring methods may interfere with or degrade the high-intensity FEL beam, posing a challenge for in-situ measurements.

Purpose of the Study:

• To develop and validate an online monitoring device for free-electron laser (FEL) wavelengths.
• To assess the capability of a novel photoionization-based spectrometer for real-time spectral property measurements of FEL pulses.
• To demonstrate that the developed device can provide essential feedback without compromising the FEL beam quality.

Main Methods:

• The online spectrometer utilizes the photoionization of gaseous targets.
• It measures the time-of-flight spectra of the resulting electrons and ions.
• Experimental studies and cross-calibration measurements were performed on the FLASH2 facility.

Main Results:

• The developed online photoionization spectrometer successfully monitored the spectral properties of the FEL pulses.
• Experimental data confirmed the device's ability to provide real-time feedback on photon energy.
• Cross-calibration measurements validated the accuracy and reliability of the spectrometer's measurements.

Conclusions:

• The online photoionization spectrometer is a viable tool for real-time monitoring of FEL wavelengths.
• This technology addresses the challenge of pulse-to-pulse fluctuations in SASE FELs.
• The spectrometer provides crucial diagnostic information for interpreting photon-matter interaction experiments without degrading the FEL beam.