Two-photon absorption in nitrobenzol

Abstract
When nitrobenzol is illuminated by an intense picosecond pump beam at nm, it displays a two-photon absorption (TPA) phenomenon which can be explained by the presence of the excited states in the calculated level diagram. The combination of TPA and optical Kerr effect leads to a strong modulation of the transmission of a probe beam in the presence of a pump beam, according to their time delay.