Photonic Crystal Laser-Driven Accelerator Structures

Abstract

Laser-driven acceleration holds great promise for significantly improving accelerating gradient.However, scaling the conventional process of structure-based acceleration in vacuum down to optical wavelengths requires a substantially different kind of structure. We require an optical waveguide that (1) is constructed out of dielectric materials, (2) has transverse size on the order of a wavelength, and (3) supports a mode with speed-of-light phase velocity in vacuum. Photonic crystals-structures whose electromagnetic properties are spatially periodic-can meet these requirements.We discuss simulated photonic crystal accelerator structures and describe their properties. We begin with a class of two-dimensional structures which serves to illustrate the design considerations and trade-offs involved. We then present a three-dimensional structure, and describe its performance in terms of accelerating gradient and efficiency. We discuss particle beam dynamics in this structure, demonstrating a method for keeping a beam confined to the waveguide.We also discuss material and fabrication considerations. Since accelerating gradient is limited by optical damage to the structure, the damage threshold of the dielectric is a critical parameter.We experimentally measure the damage threshold of silicon for picosecond pulses in the infrared, and determine that our structure is capable of sustaining an accelerating gradient of 300 MV/m at 1550 nm. Finally, we discuss possibilities for manufacturing these structures using common microfabrication techniques.v

Dielectric Laser Accelerators: Designs, Experiments, and Applications

“…Three dimensional PBG structures -such as the so-called woodpile geometry shown in Fig. 3 -have also been proposed [77,78]. The design is tailored in such a way that a TM mode is well-confined to the defect channel in the center of the photonic crystal.…”

A Traveling-Wave Forward Coupler Design for a New Accelerating Mode in a Silicon Woodpile Accelerator

“…However, this new accelerating mode still has a group velocity of only about 10% of the speed of light. This low group velocity implies the necessity of frequent injections of new drive laser pulses to the electrons, further demanding compact and easy to fabricate cou-plers [12]. The abscissa of Fig.…”