Nonlinear optical spectroscopy in the time domain: Studies of ultrafast molecular processes in the condensed phase.

摘要

Ultrafast molecular processes in the condensed phase at room temperature are studied in the time domain by four wave mixing spectroscopy. The structure/dynamics of various quantum states can be studied by varying the time ordering of the incident fields, their polarization, their colors, etc. In one, time-resolved coherent Stokes Raman spectroscopy of benzene is investigated at room temperature. The reorientational correlation time of benzene as well as the {dollar}Tsb2{dollar} time of the {dollar}nusb1{dollar} ring-breathing mode have been measured by using two different polarization geometries. Bohr frequency difference beats have also been resolved between the {dollar}nusb1{dollar} modes of {dollar}rm sp{lcub}12{rcub}Csb6Hsb6{dollar} and {dollar}rm sp{lcub}12{rcub}Csb5sp{lcub}13{rcub}CHsb6.{dollar}; The dephasing dynamics of the {dollar}nusb1{dollar} ring-breathing mode of neat benzene is studied by time-resolved coherent anti-Stokes Raman scattering. Ultrafast time resolution reveals deviation from the conventional exponential decay. The correlation time, {dollar}tausb{lcub}rm c{rcub},{dollar} and the rms magnitude, {dollar}Delta{dollar}, of the Bohr frequency modulation are determined for the process responsible for the vibrational dephasing by Kubo dephasing function analysis.; The electronic dephasing of two oxazine dyes in ethylene glycol at room temperature is investigated by photon echo experiments. It was found that at least two stochastic processes are responsible for the observed electronic dephasing. Both fast (homogeneous) and slow (inhomogeneous) dynamics are recovered using Kubo line shape analysis. Moreover, the slow dynamics is found to spectrally diffuse over the inhomogeneous distribution on the time scale around a picosecond.; Time-resolved degenerate four wave mixing signal of dyes in a population measurement geometry is reported. The vibrational coherences both in the ground and excited electronic states produced strong oscillations in the signal together with the usual population decay from the excited electronic state. Absolute frequencies and their dephasing times of the vibrational modes at {dollar}sim{dollar}590 cm{dollar}sp{lcub}-1{rcub}{dollar} are obtained.; Finally, a new inverse transform procedure is presented that calculates the absorption band (ABS) from an experimental Raman excitation profile (REP). An iterative solution is sought for an integral Hilbert transform relation. An exact ABS is recovered regardless of the starting ABS when sufficient iterations are performed.