Nonperturbative theory of femtosecond time-resolved spectroscopy: optical N-wave mixing and strong-pulse spectroscopies

• Applicant: Professor Dr. Wolfgang Domcke
• Subject Area: Theoretical Chemistry: Electronic Structure, Dynamics, Simulation ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2012 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 226726153

• Final Report Year: 2020

Final Report Abstract

In this three-year project, the basic theory of several femtosecond time-resolved spectroscopic techniques was developed beyond the current state of research. The emphasis has been on the nonperturbative description of the radiation-matter interaction, although the perturbative formalism also was used where appropriate. The equation-of-motion phase-matching approach (EOM-PMA) as well as a fully nonperturbative theoretical description of femtosecond time-resolved nonlinear signals developed earlier in the group of the applicant were implemented for femtosecond stimulated Raman spectroscopy (FSRS). The information content of FSRS signals was analysed for suitable models. The molecular models were extended from few-mode systems to multi-mode systems by considering few-state few-mode conical intersection models coupled to a dissipative environment. The hierarchy equations-ofmotion (HEOM) method and the Davydov ansatz were employed to perform exact numerical studies of the ultrafast nonadiabatic dynamics of these multi-mode systems. The HEOM method and the EOM-PMA were combined to perform numerical simulations of femtosecond time-resolved fluorescence spectra of a dissipative nonadiabatic system. Nonperturbative dipole response functions have been introduced as a novel concept for the theoretical analysis of four-wave-mixing signals generated with intense laser pulses. The spectroscopic effects of intense pulses and of chirp were analysed for the example of two-dimensional (2D) electronic spectroscopy experiments on atomic rubidium. The theory of two variants of fifth-order electronic spectroscopy, two-quantum 2D electronic spectroscopy and three-dimensional (3D) electronic spectroscopy, was elaborated in the framework of the perturbative formalism. The theory of femtosecond double-pump single-molecule spectroscopy with fluorescence detection has been worked out in the weak-field regime as well as in the strong-field regime. It was demonstrated by numerical simulations that the information content of double-pump single-molecule spectroscopy is enhanced in the nonperturbative regime. The theory was applied to the simulation and analysis of single-molecule signals which were measured earlier for individual LH2 antenna complexes. The research of this project has further advanced and widened the scope of the nonperturbative equation-of-motion formulation of short-pulse nonlinear spectroscopy. The equation-of-motion formulation of nonlinear spectroscopy represents a powerful alternative to the standard formalism based on perturbative dipole response functions. Fruitful collaborations with the groups of Professor Yang Zhao and Professor Howe-Siang Tan at NTU Singapore and with the group of Professor Frank Stienkemeier at the University of Freiburg are gratefully acknowledged.

Publications

• Resonant femtosecond stimulated Raman spectra: Theory and simulations. J. Phys. Chem. A 120, 3286 (2016)
  B. J. Rao, M. F. Gelin and W. Domcke
  
• Nonperturbative response functions: A tool for the interpretation of four-wave-mixing signals beyond third order. J. Chem. Phys. 147, 234104 (2017)
  L. Chen, E. Palacino-Gonzalez, M. F. Gelin and W. Domcke
  
• Resonant femtosecond stimulated Raman spectroscopy with an intense actinic pump pulse: Application to conical intersections. J. Chem. Phys. 146, 084105 (2017)
  B. J. Rao, M. F. Gelin and W. Domcke
  
• Theoretical aspects of femtosecond double-pump single-molecule spectroscopy. I. Weak-field regime. Phys. Chem. Chem. Phys. 19, 32296 (2017)
  E. Palacino-Gonzalez, M. F. Gelin and W. Domcke
  
• Simulation of femtosecond phase-locked double-pump signals of individual light-harvesting complexes LH2. J. Phys. Chem. Lett. 9, 4488 (2018)
  L. Chen, M. F. Gelin, W. Domcke and Y. Zhao
  
• Mapping of wave-packet dynamics at conical intersections by timeand frequency-resolved fluorescence spectroscopy: A computational study. J. Phys. Chem. Lett. 10, 5873 (2019)
  L. Chen, M. F. Gelin, Y. Zhao and W. Domcke