Dr. John Krizmanic
CRESST/USRA/NASA/GSFC
Phase Fresnel Lens Development for X-ray & Gamma-ray Astronomy
Angular resolution and effective area are two key parameters that define the performance of a telescope. Historically, X-ray and gamma-ray telescopes have not achieved the angular resolution and flux sensitivity possible at longer wavelengths due to the difficulty in collecting and focusing high-energy photons. Currently, the best imaging ability in the X-ray band is given by the Chandra telescope, which has achieved sub-arcsecond imaging below 10 keV. The use of diffractive optics, especially Phase Fresnel Lenses (PFLs), offers a path to significantly improved high-energy performance. In principle, PFLs can achieve diffraction-limited angular resolution, which is orders of magnitude better than the current state-of-the-art, with high throughput at X-ray and gamma-ray energies, and the capability of scaling to meter-size dimensions. Micro-arcsecond angular resolution in the X-ray and gamma-ray band is achievable, which would allow for the direct imaging of the event horizon surrounding Black Holes. We have successfully fabricated PFLs in silicon using Micro-Electro-Mechanical-System (MEMS) fabrication techniques in the MEMS Sensors and Actuators Lab (MSAL) at the University of Maryland and measured near diffraction-limited performance at X-ray energies at the GSFC 600-meter Interferometry Testbed. 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 applications. In this talk I will discuss the astronomical motivation for improving in X-ray and gamma-ray imaging performance, the physics principles behind diffractive optics, our fabrication and characterization of PFLs, and describe potential space-based telescopes employing these optics.