Real-time observation of full evolution of molecular unidirectional rotation via time-resolved spectroscopy.

• We apply spectroscopy to monitor the real-time full evolution of molecular UDR for N 2 molecules under ambient conditions. • The time-dependent alignment degree of the molecular UDR and 1-D alignment have different features. • The rotational Doppler shift was observed to change according to these features at various rotational revivals. Molecular unidirectional rotation (UDR) induced by femtosecond lasers has attracted significant attention in recent years. We monitored the molecular UDR for nitrogen molecules under ambient conditions in real time by observing time-resolved spectroscopic probes, based on the rotational Doppler effect. The time-dependent alignment degree of the molecular UDR was experimentally observed to differ from that of the 1-D alignment. Moreover, the rotational Doppler shift exhibited different features at various rotational revivals. Finally, we used spectroscopy to demonstrate the manifestation of the quantum nature of the molecular UDR. [ABSTRACT FROM AUTHOR]