Attosecond physics in optical near fields

Attosecond science-the control of electrons by ultrashort laser pulses-is developing into lightfield-driven, or petahertz, electronics. Optical-field-driven nanostructures provide elements for such electronics, which rely on understanding electron dynamics in the optical near field. Here we report near-field-induced low-energy stripes in carrier-envelope-phase-dependent electron spectra-a spectral feature that appears in the direct electrons emitted from a strongly driven nanostructure. These stripes arise from the subcycle sensitivity of the ponderomotive acceleration of electrons injected into a strong near-field gradient by a few-cycle optical waveform. They allow the tracking of direct and rescattered electron emissions on subcycle timescales and provide access to the electron momentum width at emission. Because this effect occurs in the direct electron signal, a large fraction of the emitted electrons can be steered, enabling the isolation of individual attosecond electron bursts with high charge density.