From random to oriented——ultrafast control of molecular rotation dynamics

Molecular orientation physics studies the manipulation of the spatial arrangement of molecules and the preparation of molecular structures with a given defined direction. In the last decade, this field has made great progress; with the help of various techniques our understanding of molecular orientation has reached a whole new level. We first describe the quantum state distribution of molecules, the methods for selecting molecular rotation quantum states, and molecular rotational dynamics, then summarize recent results on the control of molecular orientation by ultrafast coherent rotational state population. Both experiment and theory have illustrated that under the same laser excitation starts from different rotational states, different rotation wave packets are formed and the time dependent evolution of alignment and orientation are complete different. It has demonstrated that the degree of orientation for molecules can be increased by select rotational states. The use of oriented molecules as the interaction target can provide rich material for research on atomic and molecular dynamics, precision measurement, stereo-chemical reactions，and molecule-surface collision processes.