Development and application of a hybrid femtosecond/picosecond coherent Raman probe designed for study of excited state systems

The conversion from purely femtosecond coherent anti-Stokes Raman spectroscopy (CARS) to a more advantageous hybrid femtosecond/picosecond CARS (fs/ps CARS) probe for time-resolved vibrational dynamics studies is detailed. This probe provides a number of benefits for the use of studying the evolution of electronically excited states, including rapid data acquisition speeds, increased spectral resolution, and discrimination against competing background signals. The high time resolution is shown to depend on the cross correlation of the excitation pulse and initial CARS pulses while the high frequency resolution is shown to depend on the final CARS electric field. The pump-fs/ps CARS probe technique is applied to study the dynamics of several excited state systems, including coumarin 153, where it was shown that complex dynamics exist between hydrogen bonded and non-hydrogen bonded species. Additionally, the complex behavior of the excited state vibrational evolution during solvation is explored. Finally, fs/ps CARS was used to probe the ground and excited state structures of N,N-dimethyl- p-nitroaniline to study the effects of the charge transfer character on the ground and excited state molecular structure as well as the relaxation process after internal conversion