Laser Microfabrication Of THz Wakefield Structures

X-Ray free electron lasers are unique tools for investigating nanoscale structure and dynamics. These are large facilities because they require electrons to be accelerated to few GeV energies. To make them compact, an acceleration at high gradient and high frequency is proposed. However at this moment, there is no reliable fabrication method for high frequency corrugated accelerating structures. The corrugations required are on the order of 50–150 micron depth and 150–300 micron periodicity. This is combined with 2-mm inner diameter, 50-cm length and 10-micron straightness requirement. Euclid Techlabs LLC proposes a highly serial method of structure fabrication: laser ablation. The waveguide will be produced in a split block: two copper plates with corrugated half-channel ablated in them will be joined together to form the required corrugated waveguide. A combination of laser beam rastering, stage translation and inline metrology allows for precise fabrication of long corrugated waveguides. In recent years, laser micromachining has made impressive improvements in terms of accuracy, scalability and surface finish. Furthermore, the availability of femtosecond lasers yields ablation without melting. Surfaces processed in this fashion exhibit less structural damage and are expected to have a high damage threshold. In Phase I, we will produce several waveguide prototypes. We will perform extensive metrology measurements to identify and mitigate the main factors that adversely influence manufacturing tolerances. The ultimate goal of Phase I is to produce a 5-cm waveguide prototype with the required straightness and features. The goal of the project as a whole is to produce and test the full-featured, 50-cm-long corrugated waveguide. The proposed approach allows the fabrication of intricate corrugated structures for microwave components in the mm and sub-mm range. Currently such structures are fabricated in multiple steps based on semiconductor technologies that include lithography, etching and sputtering. This process is expensive and structures are limited in their size and breakdown strength. Laser microfabrication paired with online metrology is an inexpensive alternative, a perfect approach for rapid prototyping of high power THz structures for vacuum electronics and wakefield acceleration.