Extraction of accurate structure-factor amplitudes from Laue data: wavelength normalization with wiggler and undulator X-ray sources

Abstract

Wavelength normalization is an essential part of processing of Laue X-ray diffraction data and is critically important for deriving accurate structure-factor amplitudes. The results of wavelength normalization for Laue data obtained in nanosecond time-resolved experiments at the ID09 beamline at the European Synchrotron Radiation Facility, Grenoble, France, are presented. Several wiggler and undulator insertion devices with complex spectra were used. The results show that even in the most challenging cases, such as wiggler/undulator tandems or single-line undulators, accurate wavelength normalization does not require unusually redundant Laue data and can be accomplished using typical Laue data sets. Single-line undulator spectra derived from Laue data compare well with the measured incident X-ray spectra. Successful wavelength normalization of the undulator data was also confirmed by the observed signal in nanosecond time-resolved experiments. Single-line undulators, which are attractive for time-resolved experiments due to their high peak intensity and low polychromatic background, are compared with wigglers, based on data obtained on the same crystal.

Time-resolved structural studies of protein reaction dynamics: a smorgasbord of X-ray approaches

“…Two key advantages emerge from the use of a broad spectrum X-ray beam (so-called 'white' wiggler; or 'pink' undulator spectra): the first is that the maximum available X-ray flux from the synchrotron insertion device may be utilized; the second is that the broad spectrum of the X-ray beam enables a large number of full X-ray diffraction reflections to be collected (rather than partial reflections) without the need to rotate the crystal, which is essential when one wishes to record snapshots on sub-millisecond timescales. Nevertheless, this approach encompasses a large number of technical challenges which have been widely discussed (Š rajer et al, 2000;Ren et al, 1999;Yang et al, 1998;Bourgeois et al, 1996;Moffat, 2003Moffat, , 1998a, the most limiting of which is high demands regarding low mosaic spread for the crystals of interest. Since the very structural changes that one may wish to observe can induce strain within a tightly packed crystal lattice and thereby increase crystal mosaic spread, this limitation can be both a fundamental limitation as well as a practical one.…”

Analysis of multicrystal pump–probe data sets. I. Expressions for the RATIO model

“…The method is based on the ratio R of the intensities with and without light exposure I laserON =I laserOFF . It eliminates dependence on the wavelength when using the pink-Laue technique, the need for absorption corrections (Š rajer et al, 2000;Ren & Moffat, 1995) and the effect of all but very short range fluctuations in the source intensity. In previous work, we have used photo-Wilson plots to estimate temperature increases on exposure and ratio correlation plots between data sets to estimate reproducibility (Vorontsov et al, 2009;Makal et al, 2011).…”

On the assessment of time-resolved diffraction results

“…In this publication, all the indicators and tools are based on the Ratio method (Coppens et al, 2009) in which the analysis uses the ratio of the laser-on and laser-off intensities. The method eliminates dependence on the wavelength when using the pink-Laue technique, the need for absorption corrections (Š rajer et al, 2000;Ren & Moffat, 1995) and the effect of all but very short-range fluctuations in the source intensity. Indicators of agreement and Fourier difference maps for dynamic structure crystallography previously defined (Coppens et al, 2008 are discussed and complementary new definitions proposed.…”