Focusing Optics

The microprobe set-up is situated on a movable granite table in the third hutch of the ID18 beamline at about 59 m distance from the X-ray source. For the demagnification of the synchrotron source and for creating the micro-beam, parabolic Compound Refractive Lenses (CRL) are used. The CRL [1,2] is composed of different number of individual Al lenses depending on the energy of the focused beam. The typical focal distance is between 0.5-1.2 m depending on the energy of the incoming beam leaving a relatively large place between the sample and focusing device for placing e.g. beam-shaping (pin-hole) or beam monitoring (photodiode, ionization chamber) elements in between.

The size of the focused beam is typically 1-2 microns vertically and 12-15 microns horizontally.

Schematic of the Compound Refractive Lens (CRL) and the result of a knife-edge scan of an Au knife-edge sample at 21 keV energy using a CRL of 63 individual Al lenses

The intensity of the focused beam is typically  photons/sec depending on the energy of the incoming beam and on the number of undulators used. The horizontal beam-size can be decreased by closing the secondary slits but obtaining less intensity (e.g. about 5 micron horizontal beam-size with about 40% intensity). Larger spot-size can be easily obtained by defocusing the focusing CRL lens.

References:

1. Snigirev A, Kohn V, Snigireva I , Lengeler B., Nature, 384, 49-51 (1996).

2. Lengeler B, Schroer C, Tummler J, Benner B, Richwin M, Snigirev A, Snigireva I, Drakopoulos M., J. Synchrotron Radiation, 6, 1153-1167 (1999).