SBIR-STTR Award

There is great interest in having sources of short, intense pulses of Terahertz (THz) radiation to gain a better understanding, and ultimately to control, matter at the electronic, atomic, and molecular levels. This type of radiation source will be pertinent in fields as diverse as chemical and biological imaging, medical diagnostics and medical treatment, material science, telecommunications, semiconductor, and superconductor research. The next generation of THz frequency sources, as well as related instruments such as electron accelerators and wakefield accelerators, require new and improved components. Cylindrical copper waveguides, with internal corrugations, engineered to perform as slow-wave structures, are among the essential components needed. These metallic components will be used to generate and amplify THz frequency electromagnetic waves. To date, these components have only been produced in very limited quantities by end-users, by means of either extremely expensive X-ray LIGA facilities, or other approaches that lack the precision required for the intended applications. A much more cost-effective, high-precision alternative fabrication approach is required. We are proposing to use our well-established precision micromachining capability to produce sacrificial mandrels made out of fused silica glass. These exactingly-shaped mandrels will be electroplated with a thick layer of copper. Subsequent etching of the glass mandrel will result in the creation of cylindrical copper waveguides that have internal corrugations precisely engineered for the generation and amplification of THz frequency electromagnetic waves. In Phase I, we will design and fabricate waveguides with lengths up to 100-mm (4 inch). In Phase II, the fabrication hardware will be upgraded to produce waveguides with lengths up to 500-mm (20 inch) and we will test them in a relevant environment.

Over the last couple decades, powerful X-ray photon sources have been built and made available to the broad scientific community. These large (national laboratory scale) tools allow users to address some of the most important basic and applied research challenges. Even more powerful hard x-ray facilities are being designed. Many of these new facilities will rely on Wakefield accelerators to generate higher intensity / higher brightness beams. Of special importance is the Argonne Wakefield Accelerator program, which pursues the development of a variant known as electron beam-driven Structure Wakefield Accelerator (SWA). An array of accelerators based on this variant will play a central role in a free-electron laser-based x-ray user facility that is under consideration at Argonne National Laboratory. Electron beam-driven SWAs require high-precision cylindrical metallic waveguides, with internal corrugations engineered to perform as amplifying structures. Inability to procure commercial waveguides with the desired internal geometry is the major factor that has, so far, prevented the deployment of electron beam-driven SWAs. The goal of this program is to eliminate this barrier by developing a cost-effective process to fabricate high-precision cylindrical metallic waveguides with internal corrugations. The selected fabrication approach is based on the photo-chemical structuring of glass. This well-understood and very reproducible technique is used to produce sacrificial mandrels made out of fused silica. These exactingly-shaped pieces have on their external surface a pattern that corresponds to the desired internal shape (corrugation) of the SWA waveguide. A thick layer of copper is subsequently electro-deposited on the glass surface. Finally, the glass mandrel is etched away, leaving a free-standing hollowed metallic tube with precisely-shaped internal corrugations. During Phase I, the overall fabrication concept was validated. Metrology data confirmed that the desired accuracy can be achieved using the proposed approach. Several short demonstrators, based on an Argonne National Laboratory’s design, were produced. In Phase II, full size devices will be fabricated and provided to DOE end users.