Ultra-Thin Optical Diagnostic Filters for Plasma Wakefield Accelerators

65884 In plasma wakefield acceleration, electron and laser beams emerge together from the plasma. A filter is required to separate the two beams and to provide electron beam diagnostics. The filter must be thin enough, so as not to impede the electron beam, and highly reflective, in order to perform the beam separation and to resist laser damage. This project will develop the required filters through the combination of multilayer dielectric technology and ultra-thin substrate technology. Optical modeling will be used to determine filter composition, and iterative vacuum depositions will be performed to identify the fabrication parameters needed to achieve durable filters that meet the performance specifications. In Phase I, a freestanding filter, totaling less than 4 microns in physical thickness with a 21-layer dielectric reflector stack, was fabricated and tested. Reflectance exceeded expectation, demonstrating the feasibility of the filter design. Because the Phase I filter showed signs of intrinsic stress, Phase II will focus on developing production techniques that yield durable filters, optimal for the intended application. The filters will also be extensively characterized, both mechanically and optically. Commercial Applications and Other Benefits as described by the awardee: The new filters should have application to electron beam diagnostic filters, infrared band pass filters and beam splitters, adaptive optics for ground and space observatories, and filters for optical fiber communication networks.