In practice the beam spot size is not generally limited by the quality of the optical devices, but rather by other factors such as temperature stability, ambient and dynamic vibrations. For high-energy nano-focussing applications, compound refractive lens CRL chips and small radius lenses are used. For such nano-focusing applications, the optics must be mounted on the same stage as the diffractometer in order that the optics and sample vibrate in tandem.

Compound refractive lenses are an "in-line" optical focussing device that does not deviate the incoming beam path but effectively acts as a slit. This leads to an inherent stability in comparison to any of the other optics which diffract or reflect the X-ray beam. In particular, the most important ambient vibrations are "rocking' modes of optical benches. Whereas diffractive or reflective optics are very sensitive to such vibrations (the angle of the vibration is doubled in the output beam, and the amplitude increases with distance), in-line refractive optics demonstrate essentially no effect.

Figure showing i) set up of two nano lens chips, ii) magnified image of set up and iii) SEM image of the lens chip (Vaughan et al. 2011).

Each lense cartridge is comprised of 10 lens arrays, where each individual lens is 100 microns in length, with an aperture and depth of 50 microns. The arrays are optimized for the energy range 10 - 55 keV, with (5 keV step size between arrays) giving a focal distance of 10 cm. The focal distance will alter with energy.

Focusing with the in-vacuum transfocator (IVT) and nCRLs

At 92 m (i.e. in EH3), the focal spot of the IVT is slightly smaller than the nCRL aperture. This means that essentially all of the vertical beam can be refocused producing a large gain in flux for relatively little beam broadening.

Vaughan, G. B. M., J. P. Wright, A. Bytchkov, M. Rossat, H. Gleyzolle, I. Snigireva, and A. Snigirev, 2011, X-ray transfocators: focusing devices based on compound refractive lenses: Journal of Synchrotron Radiation, v. 18, p. 125-133.