  The widespread use of high energy particle beams in basic research, medicine
and coherent X-ray generation coupled with the large size of modern radio
frequency (RF) accelerator devices and facilities has motivated a strong need
for alternative accelerators operating in regimes outside of RF. Working at
optical frequencies, dielectric laser accelerators (DLAs) - transparent
laser-driven nanoscale dielectric structures whose near fields can
synchronously accelerate charged particles - have demonstrated high-gradient
acceleration with a variety of laser wavelengths, materials, and electron beam
parameters, potentially enabling miniaturized accelerators and table-top
coherent x-ray sources. To realize a useful (i.e. scalable) DLA, crucial
developments have remained: concatenation of components including sustained
phase synchronicity to reach arbitrary final energies as well as deflection and
focusing elements to keep the beam well collimated along the design axis. Here,
all of these elements are demonstrated with a subrelativistic electron beam. In
particular, by creating two interaction regions via illumination of a
nanograting with two spatio-temporally separated pulsed laser beams, we
demonstrate a phase-controlled doubling of electron energy gain from 0.7 to 1.4
keV (2.5 percent to 5 percent of the initial beam energy) and through use of a
chirped grating geometry, we overcome the dephasing limit of 25 keV electrons,
increasing their energy gains to a laser power limited 10 percent of their
initial energy. Further, optically-driven transverse focusing of the electron
beam with focal lengths below 200 microns is achieved via a parabolic grating
geometry. These results lay the cornerstone for future miniaturized phase
synchronous vacuum-structure-based accelerators.
