Measuring the temporal evolution characteristics of picosecond pulses based on cross-correlation during nonlinear propagation

When the picosecond pulse with a initial temporal modulation propagates and amplifies in the large-scale Nd:glass laser system, the temporal modulation will be accumulated and enhanced, which causes serious temporal distortion in the output picosecond pulse. The output beam quality of the whole Nd:glass laser system will become very poor due to the spatiotemporal coupling effect. So measuring the initial temporal structure and temporal evolutions of the picosecond pulse after nonlinear propagation is necessary. We propose a method of measuring the temporal characteristics of a picosecond pulse by a synchronized femtosecond pulse. This method has advantages of simple operation, convenient and high resolution. The initial temporal fine structure and temporal evolutions of the picosecond pulse passing through different lengths of CS2 nonlinear medium are measured. The results show that the initial temporal shape of the picosecond pulse is very clean and smooth. When the picosecond pulse propagates in CS2 nonlinear medium, the pulse width has a trend of slight narrow with increasing the length of CS2 nonlinear medium due to the spatiotemporal coupling effect.