Polycapillary

Polycapillary refers to an optical element consisting of a dense array of tiny hollow capillaries, typically fused glass or polymer tubes, that guides or shapes X-ray or other high-energy photon beams. The capillaries are arranged so that X-rays crossing the array undergo multiple reflections along inner walls, enabling transmission with controlled directionality. In practice, polycapillary devices are used as collimators, beam concentrators, or focusing lenses for X-ray beams.

Construction involves thousands to millions of adjacent capillaries with inner diameters from a few micrometers to tens of micrometers. The capillaries are aligned in a common geometry and embedded in a substrate. Variants include straight bundles for collimation and tapered or curved configurations for focusing; some designs use quasi-parallel channels to collect divergent beams, others use a conical arrangement to focus.

Operation relies on X-rays incident on the capillary array reflecting off inner walls within the capillaries. The overall effect can be a collimated beam, a focused spot with micrometer-scale size, or a softly divergent beam, depending on geometry. Efficiency and focal length depend on X-ray energy, capillary geometry, and manufacturing quality.

Applications span X-ray fluorescence (XRF), scanning X-ray diffraction and imaging, microfocus X-ray spectroscopy, and synchrotron beamlines. Polycapillary optics enhance flux, spatial resolution, and collection efficiency, enabling microbeam and microimaging techniques on laboratory sources or large research facilities.

History and development: Polycapillary optics were developed in the late 20th century to manipulate X-ray beams on compact scales, with ongoing improvements in uniformity, energy range, and manufacturing. They are used alongside traditional lenses and mirrors in modern X-ray instrumentation.