Extended coherent electron acceleration on a nanophotonic chip

With further advancements in the semiconductor industry, a movement to produce cheaper, smaller and less resource intensive technology is emerging. This can also be seen in research labs for particle acceleration using large scale accelerators. They require high maintenance and power consumption, and the limited beam time slows down the progress of fundamental experiments. The Accelerator on a Chip International Programm, or ACHIP, aimed to develop a low cost and compact accelerator that can be used in any lab. To achieve this, one has to take advantage of the new technologies provided by the semiconductor industry and laser science leading to a novel type of accelerator, called Dielectric Laser Accelerator (DLA). Unlike conventional accelerator technologies, which rely on radio frequency (RF) metal-based cavities and large-scale infrastructure, DLAs use high damage threshold dielectric materials and near-fields that are generated by a femtosecond laser pulse to achieve extended electron acceleration over less than a millimetre. The critical aspect of the applications, either RF or DLA, is the extended acceleration over large distances to obtain energies in the megaelectronvolt range while guiding the electrons through the accelerator. For the application with DLA, this means millimetre to centimetre long structures with a 250nm narrow guiding channel and therefore a tight tolerance for the electron beam. To ensure full control of the electrons the so-called alternating phase focusing (APF) effect comes into play. By introducing gaps in the structure, the electron beam is continuously focused or defocused in an alternating fashion in one transverse direction. At the same time maintaining phase matching with the laser-generated near-field that acts accelerating in the longitudinal direction must be ensured, such that an electron bucket forms and is accelerated coherently. This thesis aims to address these two crucial parts of efficient electron acceleration and, applied to nanophotonic structures, shows the experimental realisation. In particular, it shows the extended coherent acceleration from an initial electron energy of 28.4keV to 40.7keV in a 500micrometer long dielectric structure, i.e., an energy gain of 43%, whilst confining the beam over this long distance in an acceleration channel only 225nm wide. The experimental findings agree well with particle tracking simulations and mark the next step for the implementation of novel accelerator schemes utilising dielectric materials and femtosecond laser pulses.