飞秒时间分辨实验中泵浦-探测交叉相关函数的测量和时间零点的确定

Determine The Pump-probe Cross Correlation Function and The Zero of Time of The Pump and Probe Laser in Femtosecond Time-resolved Studies

飞秒激光技术的出现使得实时探测与跟踪激发态超快弛豫动力学过程成为可能,并能够给出激发态动力学过程清晰的物理图像。而在飞秒时间分辨实验中,泵浦-探测相关函数和时间零点直接影响实验结果的可靠性和准确性。本文结合飞秒激光在分子激发态超快动力学过程中的应用进展,介绍了根据实验条件和要求,在具体实验过程中泵浦-探测相关函数测量和时间零点确定的几种方法。实验中选择可见光作为泵浦光和探测光时,可以通过测定随泵浦-探测时间延迟变化的泵浦激光与探测激光的和频/差频光强来确定泵浦探测交叉相关函数和时间零点;而选择中心波长在紫外甚至真空紫外的激光脉冲作为泵浦光或探测光时,泵浦-探测交叉相关函数通常采用校正的方法测量。

Femtosecond laser technique, not only makes the observation of excited state relaxation processes more directly, but also offers information for disentangle the complex dynamics of excited state relaxation processes. However, what have an explosive impact on accuracy and reliability of experimental result is that cross correlation function as well as the zero of time of the pump and probe laser pulses, therefore, determine the correct value of them is the most vital process in the experi- ment. Examples of applying the femtosecond pump-probe technique is presented to study the relaxa- tion dynamics of the molecular excited states, by what, on the basis of experimental conditions and requirements, the paper introduced approaches of determine the cross correlation function as well as the zero of time of the pump and probe laser pulse in the course of concrete femtosecond time-re- solved experiments. For the pump and the probe laser pulses in the visible light range, by way ofdelay time of the pump and the probe pulses, we could apply optical technique to detect the transi- ent of the intensity of the second harmonic generation. Yet, for the determination of correlation func- tion as well as the zero of time for the ultrafast pulses in the UV or the VUV, calibration method would be an ideal method.