Coherence Properties of the Radiation from X-ray Free Electron Lasers

Mikhail Yurkov


A description of the statistical and coherence properties of the radiation from X-ray free electron lasers is one of the most complicated topics in free electron laser physics. Results of studies in this field are distributed over many papers published during the past three decades. We have made an attempt to put together all knowledge on the subject available to date. We avoid complicated mathematical derivations, and put the main emphasis on physical features and final results. Free electron laser theory has reached mature status, making it possible to present final results in an elegant form. Application of similarity techniques to the results of numerical simulations allowed us to derive universal scaling relations for the main characteristics of an X-ray free electron laser operating in the saturation regime: efficiency, coherence time, degree of transverse coherence, and pointing stability of the radiation. Statistical and coherence properties of the higher harmonics of the radiation are highlighted as well.


Free electron laser; X-ray laser; self-amplified spontaneous emission FEL; SASE FEL; statistics; fluctuations; coherence; temporal coherence; spatial coherence; harmonics.

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