arXiv subjects

D. Attwood

Publications and source records attributed to D. Attwood.

3 recordsLinked to original sources

arXiv2012

Spatial and temporal coherence properties of single free-electron laser pulses

The experimental characterization of the spatial and temporal coherence properties of the free-electron laser in Hamburg (FLASH) at a wavelength of 8.0 nm is presented. Double pinhole diffraction patterns of single femtosecond pulses focused to a size of about 10 microns by 10 microns were measured. A transverse coherence length of 6.2 microns in the horizontal and 8.7 microns in the vertical direction was determined from the most coherent pulses. Using a split and delay unit the coherence time of the pulses produced in the same operation conditions of FLASH was measured to be 1.75 fs. From our experiment we estimated the degeneracy parameter of the FLASH beam to be on the order of $10^{10}$ to $10^{11}$, which exceeds the values of this parameter at any other source in the same energy range by many orders of magnitude.

physics.optics↗

arXiv2011

Coherence Properties of Individual Femtosecond Pulses of an X-ray Free-Electron Laser

Measurements of the spatial and temporal coherence of single, femtosecond x-ray pulses generated by the first hard x-ray free-electron laser (FEL), the Linac Coherent Light Source (LCLS), are presented. Single shot measurements were performed at 780 eV x-ray photon energy using apertures containing double pinholes in "diffract and destroy" mode. We determined a coherence length of 17 micrometers in the vertical direction, which is approximately the size of the focused LCLS beam in the same direction. The analysis of the diffraction patterns produced by the pinholes with the largest separation yields an estimate of the temporal coherence time of 0.6 fs. We find that the total degree of transverse coherence is 56% and that the x-ray pulses are adequately described by two transverse coherent modes in each direction. This leads us to the conclusion that 78% of the total power is contained in the dominant mode.

physics.optics↗

arXiv2005

The scattering of muons in low Z materials

This paper presents the measurement of the scattering of 172 MeV/c muons in assorted materials, including liquid hydrogen, motivated by the need to understand ionisation cooling for muon acceleration. Data are compared with predictions from the Geant 4 simulation code and this simulation is used to deconvolute detector effects. The scattering distributions obtained are compared with the Moliere theory of multiple scattering and, in the case of liquid hydrogen, with ELMS. With the exception of ELMS, none of the models are found to provide a good description of the data. The results suggest that ionisation cooling will work better than would be predicted by Geant 4.7.0p01.

hep-ex↗