A nonperturbative calculation of nonlinear spectroscopic signals in liquid solution

Abstract

Nonlinear spectroscopic signals in liquid solution were calculated without treating the field-matter interaction in a perturbative manner. The calculation is based on the assumption that the intermolecular degrees of freedom can be treated classically, while the time evolution of the electronic state is treated quantum mechanically. The calculated overall electronic polarization is then resolved into its directional components via the method of Seidner et al. [J. Chem. Phys. 103, 3998 (1995)]. It is shown that the time dependence of the directional components is independent of laser intensity in the impulsive pulse regime, which allows for flexibility in choosing the procedure for calculating optical response functions. The utility and robustness of the nonperturbative procedure is demonstrated in the case of a two-state chromophore solvated in a monoatomic liquid, by calculating nonlinear time-domain signals in the strong-field, weak-field, impulsive, and nonimpulsive regimes.

Calculating time-resolved differential absorbance spectra for ultrafast pump-probe experiments with surface hopping trajectories

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] The interpretation and theoretical modeling of these experiments often begins with the application of perturbation theory to the fieldmatter interactions, leading to an expansion of the optical response of the molecular system in orders of the applied field, 7,8,[14][15][16][17][18][19][20][21][22][23][24][25] although nonperturbative approaches have been reported. 16,26,27 In particular, outside of anisotropic systems, nonlinear spectroscopy is dominated by third-order processes in which the system experiences three interactions with the applied electromagnetic fields. 7,8 Pump-probe experiments represent an important subset of nonlinear spectroscopy.…”

How a solute-pump/solvent-probe spectroscopy can reveal structural dynamics: Polarizability response spectra as a two-dimensional solvation spectroscopy

“…30,32,33 One approach to circumventing these problems has been to avoid linear response altogether by simulating the non-equilibrium response in the presence of explicit applied fields. [34][35][36] There have also been more recent approaches combining equilibrium and non-equilibrium trajectories. [37][38][39] Such simulations can be useful in practice, but they sacrifice the conceptual advantages of allowing us to analyze the results in terms of equilibrium average properties of the system.…”

Ultrafast Spectroscopy of Photoactive Molecular Systems from First Principles: Where We Stand Today and Where We Are Going

“…In the most general representation, the n th order polarization (with respect to the external driving field) induced in the system by the sequence of electric fields can be treated non-perturbatively by incorporating the fields into the system’s Hamiltonian. This method permits the exact numerical simulation of the dynamics of the driven system for fields of arbitrary strength and duration . The non-perturbative approach makes it possible to study, without any approximation, the effects of pulse parameters like central frequency, bandwidth, etc., including strong laser fields and temporally overlapping pulses.…”