Abstract
We study the impact of a spectral noise pedestal on the statistical properties of a self-seeded free electron laser (FEL). The broad pedestal is assumed to come from self amplified spontaneous emission (SASE) in the second stage of the self-seeding system and is uncorrelated with the narrowband amplified seed. An analytic description is developed based on the statistical theory of a one-dimensional FEL in the high gain linear regime. The theory shows good agreement with experimental data, which show that the presence of a SASE background can have a strong impact on the statistical behavior of self-seeding systems.
Highlights
Free electron lasers (FELs) use a beam of relativistic electrons to produce intense pulses of light down to hard x-ray wavelengths
FELs operate in spontaneous emission (SASE) mode, where density fluctuations from shot noise in the electron beam provide the input signal that is amplified to saturation levels
The SASE growth impacts not just the spectrum, but the statistical behavior of the output. This is one motivation for the study presented here, where we extend previous work on the statistical properties of SASE FELs to include the effects of SASE growth during self-seeding
Summary
Free electron lasers (FELs) use a beam of relativistic electrons to produce intense pulses of light down to hard x-ray wavelengths. FELs operate in SASE (self amplified spontaneous emission) mode, where density fluctuations from shot noise in the electron beam provide the input signal that is amplified to saturation levels. Originating from noise, the output pulse of SASE FELs is noisy and contains many uncorrelated temporal and frequency spikes within the. To produce a narrower and cleaner output spectrum, selfseeded FELs rely on a spectral filter (such as a grating or crystal) to isolate a narrow region of SASE frequencies for amplification [3,4]. Narrow linewidth filters (monochromators) select only a single coherent frequency spike from the SASE pulse, which has a shot-averaged bandwidth σA ≫ σm. In this case, the seed has only a single temporal mode
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