Figure 1.

Schematic drawings of some focusing devices for X-ray beams. (A) Fresnel zone plate. This is a circular grating with alternating densities. The focal distance depends on the X-ray wavelengths and white X-rays do not focus; (B) Kirkpatric-Baez (KB) mirrors. These are most commonly used for focusing X-ray beams in synchrotron radiation facilities, but are rarely used as imaging optics. The focal distance does not depend on the X-ray wavelengths and can be changed by altering the bend of the mirrors. The drawings are exaggerated.