Two-dimensional time-delayed coherent anti-Stokes Raman spectroscopy and wavepacket dynamics of high ground-state vibrations

A novel approach to the preparation and monitoring of molecules in high vibrational levels in their electronic ground state is presented. An ultrashort laser pulse prepares a well defined wavepacket in the electronic excited state and, following the evolution of this wavepacket, the proper frequency and timing are selected to optimize its coupling back down to high vibrational levels in the ground state. The evolution of the wavepacket in the ground state is then monitored by a time-delayed coherent scattering from the polarization that has been induced in the ground state by the first two pulses. The ability to populate vibrations as high as v = 26 for molecular iodine is demonstrated experimentally and the potential of the new method [which is termed (TD)2CARS] for further developments towards mode-selective excitations is discussed.