Design and development of multilayer x-ray optics

Abstract

The recent progress in the development of multilayer mirrors has revolutionized the field of astronomical X-rays optics. A variety of multilayer mirrors are now being developed for several unique applications such as hard X-ray imaging telescopes and soft X-ray polarimeters. Technology development to fabricate good quality multilayer mirrors carries a significant importance for realization of next generation X-ray instruments. In this thesis, we have presented our progress in fabricating and characterizing high quality W/B4C multilayer mirrors for various applications. We have also discussed the design and development of two X-ray instruments using the combination of grazing incidence X-ray concentrator and multilayer mirrors. We fabricated W/B4C multilayer mirrors with varied design parameters using

magnetron sputtering technique. We studied the performance and structural sta- bility of these mirrors over time and by subjecting these mirror to the temperature

variation analogous to the satellite in low earth orbit using soft X-ray, hard X-ray

reflectivity as well as scanning electron microscopic studies for estimating the con- tamination and surface quality. We observed that multilayers with small thickness

are more stable than the large thickness multilayers. We designed a multilayer mirror based soft X-ray polarimeter to operate at energies less than 1 keV. We proposed this design coupled with a hard X-ray polarimeter as a simultaneous back-end instrument to a hard X-ray telescope. For this application, to make multilayer mirrors transparent to hard X-rays, we etched the Silicon substrate of the mirrors to reduce the absorption. We observed that the etching process significantly degraded the performance of large thickness multilayers (> 5 nm) while the process did not affect the performance of short thickness multilayers (< 3 nm).