  Dielectric laser acceleration is a versatile scheme to accelerate and control
electrons with the help of femtosecond laser pulses in nanophotonic structures.
We demonstrate here the generation of a train of electron pulses with
individual pulse durations as short as $270\pm80$ attoseconds(FWHM), measured
in an indirect fashion, based on two subsequent dielectric laser interaction
regions connected by a free-space electron drift section, all on a single
photonic chip. In the first interaction region (the modulator), an energy
modulation is imprinted on the electron pulse. During free propagation, this
energy modulation evolves into a charge density modulation, which we probe in
the second interaction region (the analyzer). These results will lead to new
ways of probing ultrafast dynamics in matter and are essential for future
laser-based particle accelerators on a photonic chip.
