Nonlinear optical and chemical effects in the irradiation of liquid benzene with femtosecond pulses.

We show that a spectral resonance between the π→π* absorption band in liquid benzene and the third harmonic (TH) of a propagating 800 nm femtosecond laser beam causes large positive changes in the real refractive index at the TH wavelength. This produces an increase in the third-order optical susceptibility and leads to the enhancement of nonlinear optical effects including TH generation and self-focusing. Enhanced filamentation is observed in liquid benzene, but this effect is not seen in perdeuterated liquid benzene under similar irradiation conditions.