Real-time observation of motion and shape of the wave-packet during ultrafast lattice relaxation

利用上转换技术可以观测到飞秒时间分辨率的红外发光。本项目的目的是通过提高发光测量的时间分辨率来观察飞秒时间尺度下的波包包络的时间演化。通过激发电荷转移吸收带，研究了准一维卤素桥铂配合物中自陷激子的产生和衰减过程。我们观察到的特征振荡的发光强度在不同的能量的时间演化。在项目开始之前，时间分辨率提高到了50 fs，这几乎是世界上最好的记录，我们能够获得非常清晰的数据。在瞬态吸收等常规飞秒测量中，由于观测到的是绝热势的小范围时间响应，因此无法反演波包包络的时间发展。然而，发光方法允许我们在绝热势面上的许多不同点处获得更多的时间信息。通过对实验数据的分析和模型计算，我们成功地得到了随时间变化的波包包络。结果表明，在1/2振荡周期时，波包的空间宽度增加到初始值的2.5倍，在1个振荡周期时增加到初始值的3倍。

It is possible to observing infrared luminescence with a femtosecond time resolution, using up-conversion technique. The aim of this project is to observe time evolution of the wave-packet envelope in femtosecond time scale by improving the time resolution of the luminescence measurement. We investigated the generation and decay processes of the self-trapped excitons in the quasi-one-dimensional halogen-bridged platinum complexes by exciting the charge transfer absorption band. We observed characteristic oscillation in the time evolution of luminescence intensity at various energies. The time resolution before starting the project was improved to 50 fs, which is nearly the world best record and we were able to obtain very clear data. In the ordinary femotosecond measurements such as transient absorption, it is impossible to retrieve the time development of the wave-packet envelope, because the time response in a small range on the adiabatic potential is observed. However, the luminescence method allows us to get much more temporal information at many different points on the adiabatic potential surface. From the analysis of the experimental data based on a model calculation, we successfully retrieved the time dependent wave-packet envelope. The result shows that the spatial width of the wave-packet increases to 2.5 times of the initial value at 1/2 period and 3 times at one period of oscillation.