title: Liquid X-ray scattering with a pink-spectrum undulator.
abstract: X-ray scattering from a liquid using the spectrum from the undulator fundamental is examined as a function of the bandwidth of the spectrum. The synchrotron-generated X-ray spectrum from an undulator is 'pink', i.e. quasi-monochromatic but having a saw-tooth-shaped spectrum with a bandwidth from 1 to 15%. It is shown that features in S(q) are slightly shifted and dampened compared with strictly monochromatic data. In return, the gain in intensity is 250-500 which makes pink beams very important for time-resolved experiments. The undulator spectrum is described by a single exponential with a low-energy tail. The tail shifts features in the scattering function towards high angles and generates a small reduction in amplitude. The theoretical conclusions are compared with experiments. The r-resolved Fourier transformed signals are discussed next. Passing from q- to r-space requires a sin-Fourier transform. The Warren convergence factor is introduced in this calculation to suppress oscillatory artifacts from the finite qM in the data. It is shown that the deformation of r-resolved signals from the pink spectrum is small compared with that due to the Warren factor. The q-resolved and the r-resolved pink signals thus behave very differently.
authors.affiliation: Laboratoire de Physique Théorique de la Matière Condensée, Université Pierre et Marie Curie, 4 Place Jussieu, 75252 Paris, France.
authors.forename: S
authors.initials: S
authors.lastname: Bratos
authors.affiliation: Laboratoire de Physique Théorique de la Matière Condensée, Université Pierre et Marie Curie, 4 Place Jussieu, 75252 Paris, France.
authors.forename: J-Cl
authors.initials: JC
authors.lastname: Leicknam
authors.affiliation: European Synchrotron Radiation Facility, BP 220, 38043 Grenoble Cedex, France.
authors.forename: M
authors.initials: M
authors.lastname: Wulff
authors.affiliation: European Synchrotron Radiation Facility, BP 220, 38043 Grenoble Cedex, France.
authors.forename: D
authors.initials: D
authors.lastname: Khakhulin
keywords: X-ray scattering; liquids; pink X-rays