Attosecond timing of the dynamical Franz-Keldysh effect

To which extent dominate intra- or inter-band transitions the optical response of dielectrics when pumped by few-cycle near-infrared transient electric field? In order to find an answer to this question we investigate the dynamical Franz-Keldysh effect (DFKE) in polycrystalline diamond and discuss in details the attosecond delay of the induced electron dynamics with regards to the driving transient electric field while the peak intensity is varied between 1 to 10 × 1012 W/cm2. We found that the main oscillating feature in transient absorption at 43 eV is in phase with the electric field of the pump, to within 49 as ±78 as. However, the phase delay shows a slightly asymmetric V-shaped linear energy dispersion with a rate of about 200 as/eV. Theoretical calculations within the dipole approximation reproduce the data and allow us to conclude that intra-band motion dominates under our experimental conditions.