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

Observations in the hard X-ray and gammaray energy regimes are constrained by limited sensitivity and angular resolution. Significant gains could be made if these high-energy photons could be concentrated from a large area onto a small detector element and if diffraction-limited measurements could be obtained. Furthermore, the angular resolution in the gamma-ray band would be superior to that possible at all other wavelengths since the diffraction-limited angular resolution improves with increasing energy. Phase Fresnel Lenses (PFL’s) have high throughput at hard x-ray and gamma-ray energies, can achieve, in principle, diffraction-limited angular resolution, and have the capability of being scaled to large dimensions. We have successfully fabricated PFL’s and measured near diffraction-limited performance with high efficiency in focusing 8 keV x-rays at the GSFC 600-meter Interferometry Testbed. The results demonstrate the superior imaging potential in the x-ray/gamma-ray energy band for PFLbased optics in a format that is scalable for astronomical applications.