Theory of three-pulse photon echo spectroscopy with dual frequency combs

TL;DR

This paper provides a theoretical framework for three-pulse photon echo spectroscopy using dual frequency combs, demonstrating its equivalence to traditional methods and applying it to a model system to reproduce key spectral features.

Contribution

It introduces a comprehensive theoretical analysis of DFC-based three-pulse photon echo spectroscopy, linking it to conventional approaches and modeling spectral dynamics.

Findings

2D spectrum matches conventional four-pulse approach

Reproduces spectral features like dephasing and spectral shift

Validates the method with a solvatochromic spectral density model

Abstract

A theoretical analysis is carried out for the recently developed three-pulse photon echo spectroscopy employing dual frequency combs (DFC) as the light sources. In this method, the molecular sample interacts with three pulse trains derived from the DFC and the generated third-order signal is displayed as a two-dimensional (2D) spectrum that depends on the waiting time introduced by employing asynchronous optical sampling method. Through the analysis of the heterodyne-detected signal interferogram using a local oscillator derived from one of the optical frequency combs, we show that the 2D spectrum closely matches the spectrum expected from a conventional approach with four pulses derived from a single femtosecond laser pulse and the waiting time between the second and third field-matter interactions is given by the down-converted detection time of the interferogram. The theoretical result is applied to a two-level model system with solvation effect described by solvatochromic spectral density. The model 2D spectrum reproduces spectral features such as the loss of frequency correlation, dephasing, and spectral shift as a function of the population time. We anticipate that the present theory will be the general framework for quantitative descriptions of DFC-based nonlinear optical spectroscopy.