Dynamical behavior of ultrashort pulse laser in para-nitroaniline molecules

The electronic structures and dipole moments of para-nitroaniline molecule are calculated by use of density functional theory at ab initio level. We then investigate theoretically the interaction between the ultrashort pulse laser and the para-nitroaniline molecule medium by solving the full Maxwell-Bloch equations. The effects of permanent dipole moments on the pulse reshaping, the spectrum components, and the evolutions of energy state populations are discussed in detail. The results show that the standing slowly varying envelope and the rotating-wave approximations fail to give a good description for the propagation of an ultrashort pulse in the molecule medium. Furthermore, the dipole moments of the molecule make the propagation deviate from the area theorem further and make the pulse split more quickly. When the pulse with the excitation energy of the charge-transfer state propagates in the para-nitroaniline molecule medium, the second-harmonic spectral component appears obviously and becomes stronger as the propagating distance increases, which displays the high two-photon absorption properties of the molecule.