Coherence properties of the radiation from X-ray free electron laser

• Published in: Optics communications 2008-03, Vol.281 (5), p.1179-1188
• Main Authors: Saldin, E.L., Schneidmiller, E.A., Yurkov, M.V.
• Format: Article
• Language: English
• Subjects: Coherence; Electromagnetism; electron and ion optics; Exact sciences and technology; Free electron laser; Free-electron lasers; Fundamental areas of phenomenology (including applications); Lasers; Optics; Physics; Radiation by moving charges; Wave optics; X- and γ-ray lasers
• ISSN: 0030-4018; 1873-0310
• DOI: 10.1016/j.optcom.2007.10.044

We present a comprehensive analysis of coherence properties of the radiation from X-ray free electron laser (XFEL). We consider practically important case when XFEL is optimized for maximum gain. Such an optimization allows to reduce significantly parameter space. Application of similarity techniques to the results of numerical simulations allows to present all output characteristics of the optimized XFEL as functions of the only parameter, ratio of the emittance to the radiation wavelength, ϵˆ=2πϵ/λ. Our studies show that optimum performance of the XFEL in terms of transverse coherence is achieved at the value of the parameter ϵˆ of about unity. At smaller values of ϵˆ the degree of transverse coherence is reduced due to strong influence of poor longitudinal coherence on a transverse one. At large values of the emittance the degree of transverse coherence degrades due to poor mode selection. Comparative analysis of existing XFEL projects, European XFEL, LCLS, and SCSS is presented as well.