US Patent 10241347 Self-aligned spatial filter

A spatial filter is made by forming a structure comprising a focusing element and an opaque surface, the opaque surface being disposed remotely from the focusing element in substantially the same plane as a focal plane of the focusing element; and by forming a pinhole in the opaque surface at or adjacent to a focal point of the focusing element by transmitting a substantially collimated laser beam through the focusing element so that a point optimally corresponding to the focal point is identified on the opaque surface and imperfection of the focusing element, if any, is reflected on the shape and position of the pinhole so formed.