Study On The Control Of The Rotational Dynamics Of Gas Molecules Using Two-dimensional Rotational Coherence Spectroscopy

Rotational coherence spectroscopy has a very important position and application prospects in the study of spectroscopy analysis.In recent years,rotational coherence spectroscopy has been applied to the study of biological macromolecules and clusters,and has become an important means of spectroscopy measurement.Femtosecond laser pulses,due to their narrow pulse width and good coherence,can be used to control and study the ultrafast dynamics of molecules.In this paper,the shaping femtosecond laser pulse combined with two-dimensional rotational coherence spectroscopy is used to control and detect the coherent rotational dynamics of molecules.By adjusting the shaping pulse parameters and gradually changing the pump double pulse delay,we measure the corresponding recurrence signal using the balanced weak field detection,and study the coherent control on the rotational dynamics irradiated by two orthogonal double pulses and horizontally polarized double pulses with adjustable delay.We find that the recurrence signal gradually changes with the increase of the pump pulse delay,and the recurrence signal has superposition property,that is,the overall recurrence signal is the superposition of recurrence signals induced by the two sub-pulses in the pump pulse independently.From the two-dimensional rotational coherence spectra,we observe that the excitation process of each rotational state periodically oscillates with the delay of the pump pulse,which indicates the interference effect between the time-domain wave packets.We combine the stimulated Raman process with the spectral phase interference,and simulate the two-dimensional rotational coherence spectrum under the irradiation of the shaped femtosecond laser pulse.The experimental results are consistent with the simulation results.We believe that the coherence of the laser is well transmitted to the rotational wave packet of the molecule,and the rotational population can be controlled by the interference of the rotational dynamic excitation process.We also obtain the two-dimensional rotational coherence spectrum of the N₂O molecule through the double-pump pulse with pump detection method.The high-order response of the wave packets generated by different transition processes to the pump pulse is analyzed,and the information of the multi-step transition process is obtained.It enables us to have a deeper understanding of the recurrence structure caused by different coherent transition processes.This scheme enables us to study the evolution of the time dynamics of the rotational wave packet and the potential Raman transition process at the same time in a single experiment.This provides us with a tool to track the coherent control process.