title: Hanbury Brown-Twiss interferometry at a free-electron laser.
abstract: We present measurements of second- and higher-order intensity correlation functions (so-called Hanbury Brown-Twiss experiment) performed at the free-electron laser (FEL) FLASH in the non-linear regime of its operation. We demonstrate the high transverse coherence properties of the FEL beam with a degree of transverse coherence of about 80% and degeneracy parameter of the order 10(9) that makes it similar to laser sources. Intensity correlation measurements in spatial and frequency domain gave an estimate of the FEL average pulse duration of 50 fs. Our measurements of the higher-order correlation functions indicate that FEL radiation obeys Gaussian statistics, which is characteristic to chaotic sources.
authors.affiliation: Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Singer
authors.forename: U
authors.initials: U
authors.lastname: Lorenz
authors.forename: F
authors.initials: F
authors.lastname: Sorgenfrei
authors.forename: N
authors.initials: N
authors.lastname: Gerasimova
authors.forename: J
authors.initials: J
authors.lastname: Gulden
authors.forename: O M
authors.initials: OM
authors.lastname: Yefanov
authors.forename: R P
authors.initials: RP
authors.lastname: Kurta
authors.forename: A
authors.initials: A
authors.lastname: Shabalin
authors.forename: R
authors.initials: R
authors.lastname: Dronyak
authors.forename: R
authors.initials: R
authors.lastname: Treusch
authors.forename: V
authors.initials: V
authors.lastname: Kocharyan
authors.forename: E
authors.initials: E
authors.lastname: Weckert
authors.forename: W
authors.initials: W
authors.lastname: Wurth
authors.forename: I A
authors.initials: IA
authors.lastname: Vartanyants