Junior research group Theoretical Chemistry

Dassia Egorova

Ultrafast Dynamics and Time-resolved Spectroscopy



Time-resolved nonlinear spectroscopy

There is a huge variety of experimental techniques in the field of time-resolved optical spectroscopy. The easiest to interprete is time-resolved fluorescence: the emitted photons (recorded as a funtction of time) reflect directly the ultrafast dynamics in optically bright electronic states. But it is the hardest to detect experimentally. That is why a number of the so-called four-wave mixing (4WM) techniques has been developed. They include transient transmittance pump-probe, time-resolved coherent anti-Stokes Raman scattering (CARS), two- and three-pulse photon echo, transient grating, etc. In particular two-dimensional (2D) electronic photon-echo spectroscopy is especially sensitive and allows to monitor the system coherences in real time.

wave-packet dynamics vs. time-resolved fluorescence

Although experiments provide an immense amount of information, it is indirect and requires a detailed analysis for an unambiguous interpretation. The measured signals depend both on the system dynamics and on the laser pulse properties, and proper simulations are necessary to facilitate interpretation of experimental results, and to provide guidance for further investigations.
We develop and employ novel efficient methods for calculation of the time- and frequency-resolved optical signals. The methods allow for system Hamiltonians of arbitrary complexity, have no limitations with respect to pulse durations and automatically account for pulse-overlap effects. We are able to accurately and efficiently calculate observables of all the most frequently employed investigation schemes. Our most universal tool is the equation-of- motion phase-matching approach (EOM-PMA). It allows for a straightforward calculation of any N-wave mixing signal and can be implemented within various dynamical descriptions based either on density-matrix or wave-function formalisms. EOM-PMA has been implemented for simulations of homodyne and heterodyne two-dimensional photon-echo signals by several research groups.

Selected Papers:

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