A nanotube based device for guiding a beam of x-rays, photons, or neutrons, includes a beam source and at least one nanotube. Each nanotube has an optical entrance positioned in a manner that a projection of the direction of the central axis at the optical entrance intersects with the beam source. Each nanotube may have an interior diameter that varies along the length of the nanotube. to point the entrances of a bundle of nanotubes toward a point-shaped beam source, the bundle can be grown as an array of multilayer nanotubes from a spherical growth plate. The clear aperture of the bundle is enhanced by providing a smaller number of wall layers of each nanotube near the growth plate than at a distance from the growth plate.