Novel Fabrication of A 17-Layer 3D Silicon-Based Woodpile Structure for Dielectric Laser-Driven Accelerator
Recently, charged particles accelerated by microwave radiation are generated in large klystrons, which are called Radio frequency (RF) accelerators. However, this RF accelerator is very expensive and requires large amounts of land to bury accelerator systems in the ground. Accelerator physicists have studied high acceleration gradients. If we have a high acceleration gradient, we can get high accelerated electrons in a much shorter distance. We believed particle accelerators benefit from the high energy density provided by lasers at optical and infrared wavelengths and dielectric materials replace the metallic waveguides allowing us to utilize the high peak powers available in laser. To realize this jump from microwave to infrared wavelengths, we need decreases of 10,000 times in wavelength, and entirely new fabrication technologies to make 3D photonic crystals. 3D photonic crystals (3D PhCs) have many desirable attributions due to their abilities to confine light in all directions. The major challenge is to fabricate 3D micro/nano-structures with high yield and fast turn-around time, especially when the number of layers is large. The layer-by layer technique allows arbitrarily-shaped 3D structures to be fabricated and takes advantages of well-established integrated circuit processing techniques. Nevertheless, the complicated and lengthy procedure, in addition to roughness and/or incidental damages on the final structure by frequent dry etching, polishing, and heating, make it difficult for prototyping novel multilayer structures. Here we present a new approach to form 3D structures by transferring and stacking pre-patterned, free-standing silicon membranes and demonstrate the process by fabricating an woodpile 3D PhC, which has a complete 3D photonic band gap, and a relatively simple structure. It consists of layers of dielectric rods in the air, with the rods in each layer rotated 90 degrees. These photonic crystals can be the building blocks of next generation high-gradient accelerators.
Qi, Purdue University.
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