Fabrication of Binary Phase Photon Sieves

This NASA invention is an innovative process for fabricating high-area binary phase photon sieves with improved optical efficiency for EUV imaging applications. Binary phase photon sieves have been demonstrated for a variety of optical and x-ray applications. Photon sieves must be wide, super-thin, and etched with precise holes to refract light. Each step in NASA's photon sieve fabrication process includes considerations to protect the resulting sieves, such as leaving a honeycomb of thicker material to support the membrane and prevent tearing. The process starts by using a silicon-on-insulator wafer, includes pattern and etch-sieve pattern, and ends with a released photon sieve. The inventors have produced an 8 cm-diameter silicon sieve that is 100 nm thick including hole sizes of 2 µm in diameter with 2 µm spacing. Additionally, a similar structure has been demonstrated in niobium, with 8 cm in diameter with the same silicon hexagonal support frame. This novel process enables the fabrication of photon sieves for EUV imaging applications. While the process was initially developed to fabricate photon sieves for solar science and astronomy, it could also be used to generate metamaterial/frequency selective surface structures from the UV to THz frequency ranges. This NASA invention is a Technology Readiness Level (TRL) 4 (prototype validation in a laboratory environment) technology and is available for patent licensing. Conventional methods for focusing extreme ultraviolet (EUV) light are challenged by its high energy and short wavelength, which result in chromatic aberrations and material limitations. Photon sieves, which utilize perforated membranes, offer a solution for EUV applications requiring large-area structures. Achieving higher optical efficiency demands that the opaque region of a binary amplitude sieve to be thin enough to allow transparency while still enabling the necessary phase shift. In EUV applications, submicron-thick membranes help mitigate high material losses, but fabricating sieves with small features – such as 2 µm openings with 2 µm gaps — remains a significant challenge. To address these limitations, innovators at NASA’s Goddard Space Flight Center have developed a method for fabricating binary phase photon sieves using silicon and niobium to achieve precise focus and high-resolution imaging in applications like solar observation.