Selective nonlinear response preparation using femtosecond spectrally resolved four-wave-mixing

Area of Science:

• * Physical Chemistry
• * Chemical Physics
• * Spectroscopy

Background:

• * Homodyne degenerate four-wave-mixing (HD-FWPM) is a technique used to study molecular dynamics.
• * Assigning vibrational coherence and distinguishing it from polarization interference in HD-FWPM spectra can be challenging.
• * Understanding vibrational coherence dynamics is crucial for elucidating molecular excited-state and ground-state processes.

Purpose of the Study:

• * To present a novel method for assisting the assignment of vibrational coherence in HD-FWPM.
• * To exploit the dependence of vibrational coherence dynamics on excitation pulse sequences.
• * To enable the separation of population dynamics and vibrational coherence dynamics within a single response pathway.

Main Methods:

• * Exploitation of the interaction sequence of chirped pump and Stokes excitation pulses.
• * Combination of chirped excitation with variable delays between pump and Stokes pulses.
• * Numerical simulations performed within the response function framework.

Main Results:

• * Distinguished quantum beating from polarization interference by analyzing vibrational coherence dynamics.
• * Achieved controlled excitation of response pathways from a single electronic state.
• * Successfully separated population dynamics and vibrational coherence dynamics.
• * Demonstrated applicability to oscillatory contributions from both excited and ground electronic states.

Conclusions:

• * The presented method effectively assists in assigning vibrational coherence in HD-FWPM.
• * The approach allows for the controlled manipulation and separation of molecular dynamics.
• * Experimental validation in three polyatomic molecules confirms the method's utility.