Dear Herman On 24 April 2014 22:32, <herman.schreu...@sanofi.com> wrote:
> > > The X-ray coherent length is depending on the crystal, not the synchrotron > and my gut feeling is that it is at least several hundred unit cells, but > here other experts may correct me. > > > I assume you meant that the coherence length is a property of the beam (e.g. for a Cu target source it's related to the lifetime of the excited Cu K-alpha state), not the crystal, e,g, see http://www.aps.anl.gov/Users/Meeting/2010/Presentations/WK2talk_Vartaniants.pdf(slides 8-11). The relevant property of the crystal is the size of the microdomains. You don't get interference because coherence length << domain size, i.e. the beam is not coherent over more than 1 domain. This is true for in-house sources & synchrotrons, I guess for FELs it's different, i.e. much greater coherence length? This relates to a question I asked on the BB some time ago: if the coherence length is long enough would you start to see the effects of interference in twinned crystals, i.e. would the summation of intensities break down? I defer to the experts on synchrotrons & FELs! Cheers -- Ian
