Femtosecond spectroscopy from the perspective of a global multidimensional response function

Area of Science:

• Physical Chemistry
• Spectroscopy
• Optics

Background:

• Multidimensional response functions like nonlinear optical susceptibility are key in nonlinear optical spectroscopy.
• These functions determine nonlinear polarization from arbitrary excitations.
• Current methods focus on microscopic polarization, not directly observable macroscopic quantities.

Purpose of the Study:

• To extend the use of multidimensional response functions to directly observable macroscopic quantities.
• To introduce and explore the applications of the global response function formalism.
• To provide a generalized framework for understanding nonlinear optical phenomena.

Main Methods:

• Applying perturbation theory to expand measured quantities in a power series of the exciting field.
• Introducing a global response function for each order of perturbation, analogous to nonlinear susceptibility.
• Utilizing multidimensional spectroscopy (2D and 3D) for measuring global multidimensional response functions.

Main Results:

• The global response function formalism is applicable to macroscopic observables like radiated electric fields, fluorescence rates, and photochemical reaction rates.
• It allows for a more general derivation of results, such as the independence of stationary signals from spectral phase in the weak field limit.
• Second- and third-order responses can be precisely measured using 2D and 3D spectroscopy, respectively, considering pulse shapes.

Conclusions:

• The global response function is a versatile tool for deriving general results in nonlinear optical spectroscopy.
• It offers a unified approach for both microscopic polarization and macroscopic observable quantities.
• This formalism will aid in the development of future experimental schemes for femtosecond spectroscopy.