Hi Paul, I probably have as much experience with micro-XAFS as anyone on this list, and am willing to make a few comments. First, Steve Heald and Dale Brewe at APS/PNC-CAT have extensive experience making and using single capillaries for focussing -- probably more than anyone else. They're really the people to ask. Second, I believe there is not a commercial supplier of suitable capillaries, and that Heald and Brewe made essentially all of their own capillaries. After a few years of experience, I believe they could get 1 micron spots fairly routinely. Third, I think the consensus is that capillaries don't work too well for EXAFS. I wouldn't be willing to say that PNC-CAT has abandoned them, but I haven't seen capillaries used for this purpose in a long time. Without going into the details of the problems here, I can say that we at GSECARS and Heald etal at PNC-CAT regularly use 10cm long KB mirrors to focus APS undulator A to 2-3 microns for micro-XAFS, and that other beamlines at APS and other sources use such mirrors for micro-beam work as well. Fourth, Micro-EXAFS with a 1 micron beam and a 1 micron sample is challenging because of sample vibrations. But as the sample and spot size get to 5 to 10 microns, it works reasonably well. Many problems that appear to need 1 micron can get by with 5 microns, especially when the penetration depth is considered. Fifth, getting below 10 microns is heavily dependent on source characteristics, especially divergence. A 4m in vacuum undulator is an excellent start, but you might need to remove the larger beamline mirrors and slit down the source to get to 1 micron. Finally, It might be worth considering taking your experiment to an existing micro-EXAFS beamline, or visiting one ahead of time. ;). --Matt On Thu, 29 Apr 2004, Paul Fons wrote:
Continuing in the vein of marginally relevant questions (you need to take data before you can analyze it with horae!), I have yet another question. To make life more exciting, I would like to take a 4 m in vacuum undulator beamline that has a focussing mirror with a 250x600 micron spot size and focus down as much of the beam as I can to dimensions on the order of a micron (or a little bit bigger) using a monocapillary. I would then like to do microexafs with this setup. The brilliance of the undulator is about 5x10^15 in the range I am interested in (about 11-12 keV). Has anyone had any experience with this sort of focussing and might you recommend a company or spec to try? Thanks in advance.
Paul