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Phase Fresnel Lens Development for X-ray and Gamma-ray Astronomy

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posted on 2023-11-30, 20:28 authored by John Krizmanic, Gerald Skinner, Zaven Arzoumanian, Vlad Badilita, Neil Gehrels, Keith Gendreau, Reza Ghodssi, Nicolas Gorius, Brian Morgan, Lance Mosher, Robert Streitmatter
In principle, diffractive optics, particularly Phase Fresnel Lenses (PFLs), offer the ability to construct large, diffraction-limited, and highly efficient X-ray/$\gamma$-ray telescopes, leading to dramatic improvement in angular resolution and photon flux sensitivity. As the diffraction limit improves with increasing photon energy, gamma-ray astronomy would offer the best angular resolution over the entire electromagnetic spectrum. A major improvement in source sensitivity would be achieved if meter-size PFLs can be constructed, as the entire area of these optics focuses photons. We have fabricated small, prototype PFLs using Micro-Electro-Mechanical Systems (MEMS) fabrication techniques at the University of Maryland and measured near diffraction-limited performance with high efficiency using 8 keV and higher energy X-rays at the GSFC 600-meter Interferometry Testbed. A first generation, 8 keV PFL has demonstrated imaging corresponding to an angular resolution of approximately 20 milli-arcseconds with an efficiency $\sim$70$\%$ of the theoretical expectation. The results demonstrate the superior imaging potential in the X-ray/$\gamma$-ray energy band for PFL-based optics in a format that is scalable for astronomical instrumentation. Based upon this PFL development, we have also fabricated a `proof-of-principle' refractive-diffractive achromat and initial measurements have demonstrated nearly uniform imaging performance over a large energy range. These results indicate that the chromaticity inherent in diffractive optics can be alleviated.



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