We report a Keldysh-like model for the electron transition rate in dielectrics under an intense circularly polarized laser. We assume a parabolic two-band system and the Houston function as the time-dependent wave function of the valence and conduction bands. Our formula reproduces the experimental result for the ratio of the excitation rate between linear and circular polarizations for $alpha$-quartz. This formula can be easily introduced into simulations of nanofabrication using an intense circularly polarized laser.
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