Abstract
A theoretical investigation is reported describing the dynamical Franz-Keldysh effect (DFKE) in femtosecond
time resolution, that is, the time-dependent modulation of a dielectric function under an irradiation
of an intense laser field. Two distinct approaches are developed for a pump-probe formalism:
first-principles simulation based on real-time time-dependent density functional theory and analytic consideration
of a simple two-band model. While time-average modulation may be reasonably described by
the static Franz-Keldysh theory, a remarkable subcycle modulation and the phase shift is found to appear
be- tween the dielectric response and the applied electric field for linear polarization. In contrast, the
subcycle modulation of the dielectric function, a significant feature of the Tr-DFKE, disappears for circularly
polarized laser.
