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• Shot-to-shot wavelenght characterization

UNIEXP Research FEL Physics and Instrumentation Development Shot-to-shot wavelenght characterization  · 

Shot-to-shot wavelenght characterization

The free-electron laser FLASH produces pulses of extreme intense, coherent, linear polarized soft X-ray light pulses with repetition frequencies of up to 1 MHz. The photon generating Self-Amplifying Spontaneous Emission (SASE) process results in statistical fluctuations in all beam properties like the photon energy, which varies around 1%-2% on average and limits the resolution of spectroscopic experiments. Monochromators [1], which reduces the flux substantially and make spectroscopic experiments on very dilute target inefficient or impossible, or the measurement of the photon pulses wavelength distribution in parallel are the only possibilities to enhance experimental resolution.
For the later we developed a a compact spectrometer for shot-to-shot wavelength characterization for FLASH in cooperation with the Paul Scherrer Institut (PSI) and DESY. [2] It is based on the fast GOTTHARD detector [3] and allows the shot-to-shot wavelength spectroscopy of FEL pulses behind transparent experiments for online observation and coorelation to experimental data in the evaluation.

Realtime movie of a small selection of the data recorded during the commissioning of the spectrometer. The images show 100 frames of the single line detector recorded with a readout frequency of 200 kHz. After some non-illuminated frames, the spectra of all pulses of the pulse trains are shown. Per bunch train FLASH produced 80 electron bunches with a frequency of 200 kHz. The 13th electron bunch is kicked out before the undulator resulting in a gap of the photon pulse train in frame 23. The pulse spectra show the expected SASE related fluctuations in intensity, shape, mean wavelength and mode contributions.

[1] M. Martins et. al., Rev. Sci. Instrum. 77, 115108 (2006)
[2] S. Palutke et. al., Rev. Sci. Instrum. 86, 113107 (2015)
[3] A. Mozzanica et. al. 2012 JINST 7 C01019