  Energy transfer processes from a high-intensity ultrashort laser pulse to
electrons in simple dielectrics, silicon, diamond, and $\alpha$-quartz are
theoretically investigated by first-principles calculations based on
time-dependent density functional theory (TDDFT). Dependences on frequency as
well as intensity of the laser pulse are examined in detail, making a
comparison with the Keldysh theory. Although the Keldysh theory reliably
reproduces the main features of the TDDFT calculation, we find some deviations
between results by the two theories. The origin of the differences is examined
in detail.
