ИСТИНА

We studied the interaction of an intense THz pulse with the n-doped Si sample under the conditions inaccessible to quasi-stationary electric fields. In this work we observed that transmission by energy of the 700 fs THz pulse through n-doped Si sample amounts to as high as ∼ 8% with field strength up to 5–7 MV/cm and then gradually decreases nearly twofold at higher electric fields of 10–20 MV/cm. Analysis of the transmitted pulse waveform demonstrated its strong distortions and generation of higher frequency spectral components at 7–10 MV/cm, and finally a 300-fs single-cycle pulse was observed at a maximum field. Simulations showed that with ETHz ∼5–7 MV/cm saturation of the electron-phonon collision rate occurs, and THz transmission saturates. Generation of a single-cycle pulse at even higher fields was associated with formation of a thin ionized layer at the front sample’s surface during the first intense oscillation of the THz field cutting out subsequent field oscillations and decreasing total transmission.