A novel method to adjust the spatio-temporal superposition between two femtosecond laser pulses

To achieve accurate spatio-temporal superposition between two femtosecond laser pulses,a CCD imaging system was used to adjust the spatial superposition of both the beams and an energy meter was applied to measure the core energy of the probe pulses so that the temporal separation between the pulses could be adjusted.The dependence of the core energy on the time delay and the corresponding plasma fluorescence distribution were obtained.The experimental result proves that this method can achieve a higher time accuracy(femtosecond scale) than the traditional method,even when the crossing angle between the two femtosecond laser beams is vertical.