3.1.2.5 Capillary lenses

Capillary lenses act as transducers of the x-rays, which are totally reflected several times in the inner surface of the capillary and redirected towards the lens exit aperture. The capillaries can be bent as to conduct the x-rays into different directions. As the condition for total reflection is fulfilled only for energies below certain maximal critical energy the larger the curvature the lower energies are transduced to the exit.

If multiple elliptically shaped lenses are assembled together as to have their final directions converging into the same virtual spot, x-rays can be focused.

Straight capillaries can produce low intensity beams with sub micrometre exit spot size, whereas poli-capillary lenses have typical input and exit focus spot sizes between 6 and 100 microns and an intensity gain of several hundred times, as compared to the intensity resulting from using a pin-hole collimator of the same size.