Direct retrieval of Kerr and plasma effects from alignment-induced spatiotemporal modulation.

We developed a direct measurement method for comprehensive analyses of Kerr and plasma effects that cooperated or competed with molecular alignment-induced spatiotemporal modulation for intense aligning and weak probing pulses around zero time delay. The mixed influences were revealed by time-resolving the combined spatial focusing or defocusing dynamics under different molecular alignment directions and degrees. The nonlinear refractive index and plasma density were extracted straightforwardly, facilitating accurate explorations on multiphoton ionization and nonlinear optical Kerr effects of aligned molecular gases.