Photonic crystal laser-driven accelerator structures

TL;DR

This paper explores the design, simulation, and experimental considerations of photonic crystal structures for laser-driven particle acceleration, achieving high gradients with potential for microfabrication.

Contribution

It introduces novel photonic crystal accelerator structures supporting optical mode propagation, with detailed simulations, experimental damage threshold measurements, and fabrication considerations.

Findings

Achieved an accelerating gradient of 300 MV/m at 1550 nm.

Designed 2D and 3D photonic crystal structures for acceleration.

Measured silicon damage threshold for picosecond infrared pulses.

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.