Field induced phase transition in the few photon regime

Some features of the field induced phase transition accompanied by the vacuum creation of an electron-positron plasma (EPP) in strong time-dependent electric fields have been discussed in the work [1] in the domain of the tunneling mechanism ($\omega \ll m$, where $\omega$ is the characteristic frequency of the external field and $m$ is the electron mass). In the present contribution the features of the this process will be considered in the few photon domain where $\omega \sim m$. We observe a narrowing of the transient domain of the fast oscillations and, mainly, a considerable growth of the effectiveness of the EPP production. Under these circumstances, we see an increase of the effectiveness of the EPP creation in the particular case of a bifrequent excitation, where both mechanisms (tunneling and few photon) act simultaneously [2,3].