Kirkpatrick Baez mirror

A Kirkpatrick-Baez mirror, or KB mirror for short, focuses beams of X-rays by reflecting them at grazing incidence off a curved surface, usually coated with a layer of a heavy metal. It is named after Paul Kirkpatrick and Albert Baez, the inventors of the X-ray microscope.

KB mirrors are needed because it is not possible to make refractive lenses for X-rays. Typically they are used in pairs - one to focus horizontally and one for vertical focus. When the horizontal and vertical focuses coincide, the X-ray beam is focused to a point.