  Time-domain analysis of harmonic fields with sub-cycle resolution is now
experimentally viable due to the emergence of sensitive, on-chip techniques for
petahertz-scale optical-field sampling. We demonstrate how such a time-domain,
field-resolved analysis uncovers the extreme nonlinear electron dynamics
responsible for high-harmonic generation within solids. Time-dependent density
functional theory was used to simulate harmonic generation from a solid-state
band-gap system driven by near- to mid-infrared waveforms. Particular attention
was paid to regimes where both intraband and interband emission mechanisms play
a critical role in shaping the nonlinear response. We show that a time-domain
analysis of the harmonic radiation fields identifies the interplay between
intra- and interband dynamical processes underlying the nonlinear light
generation. With further analysis, we show that changes to the dominant
emission regime can occur after only slight changes to the peak driving
intensity and central driving wavelength. Time-domain analysis of harmonic
fields also reveals, for the first time, the possibility of rapid changes in
the dominant emission mechanism within the temporal window of the driving pulse
envelope. Finally, we examine the experimental viability of performing
time-domain analysis of harmonic fields with sub-cycle resolution using
realistic parameters.
