Bifocal photon sieve imaging in the hard x-ray region

Hard x-rays are widely used for plasma diagnosis, nondestructive inspection, and high-resolution x-ray imaging. A typical x-ray source is a tabletop micro-focus x-ray source. Here, a bifocal photon sieve (PS) with the smallest diameter of 59.6 nm was designed and fabricated by electron-beam lithography to focus hard x-rays on variable-resolution array images. An imaging experiment at 8.39 keV demonstrates that the designed and fabricated PS has two different focal lengths. The numerous pinholes that can be optimized provide richer degrees of freedom to realize considerably more functionalities. A multi-focal PS provides the possibility of splitting x-rays and further extends interferometry from visible light to hard x-rays.