Resonant laser-plasma excitation of coherent THz phonons under extreme conditions of femtosecond plasma formation in a bulk of fluorine-containing crystals

Abstract

The dynamics of coherent phonons in fluorine-containing crystals under plasma formation were studied using a nonlinear pump–probe technique based on third harmonic generation. In LiF crystal more than one phonon mode was observed. The modes are the overtones of a fundamental wave with a frequency of 0.38 THz. In CaF2 crystal phonons with frequencies of 1 and 0.1 THz were observed. In BaF2 crystal, in addition to coherent phonons with frequencies of 1 THz and 67 GHz, a significant increase of amplitude in the phonon modes with a time delay of 15 ps was detected.