Cross phase modulation artifact in liquid phase transient absorption spectroscopy

We present experimental results for the cross phase modulation (xpm) induce d transient absorption signal in a 1 mm thick fused silica plate using a wh ite light continuum as a probe. The fused silica plate mimics the entrance window of a commercial flow cell commonly used in liquid-phase transient ab sorption measurements. The experimental results are compared with those obt ained theoretically by numerically solving the set of nonlinear coupled wav e equations describing the propagation of the pump and the probe. The simul ations allow for the different group velocities of the pump and probe pulse s, and include the influence of the first and second order dispersion on th e continuum probe. From the calculations the physical origin of the complex oscillatory feature observed around the zero time delay of each wavelength of the (chirped) continuum has been accurately identified. The influence o f propagation effects arising from the finite thickness of the sample is di scussed in great detail, and the necessity to work with thin samples, prefe rably free-flowing jets, is emphasized. The good agreement between theory a nd experiment indicates that the xpm artifact may be useful for characteriz ing the continuum probe, in particular its chirp. (C) 2000 American Institu te of Physics. [S0021-8979(00)08004-X].