Isolating the chiral contribution in optical two-dimensional chiral spectroscopy using linearly polarized light

TL;DR

This paper introduces a method to isolate chiral signals in two-dimensional optical spectroscopy by adjusting the polarization angles of input pulses, effectively removing achiral background signals in common experimental setups.

Contribution

It provides analytic formulas and a perturbative approach to optimize polarization angles for eliminating achiral signals in 2D chiral spectroscopy configurations.

Findings

Achiral background signals can be eliminated by small polarization angle adjustments.

Derived analytic expressions guide polarization tuning to isolate chiral signals.

Method applicable to various experimental configurations beyond BOXCARS and GRAPES.

Abstract

The full development of mono- or multi-dimensional time-resolved spectroscopy techniques incorporating optical activity signals has been strongly hampered by the challenge of identifying the small chiral signals over the large achiral background. Here we propose a new methodology to isolate chiral signals removing the achiral background from two commonly used configurations for performing two dimensional optical spectroscopy, known as BOXCARS and GRadient Assisted Photon Echo Spectroscopy (GRAPES). It is found that in both cases an achiral signal from an isotropic system can be completely eliminated by small manipulations of the relative angles between the linear polarizations of the four input laser pulses. Starting from the formulation of a perturbative expansion of the signal in the angle between the beams and the propagation axis, we derive analytic expressions that can be used to estimate how to change the polarization angles of the four pulses to minimize achiral contributions in the studied configurations. The generalization to any other possible experimental configurations has also been discussed. %We derive analytic expressions to changes required to the polarizations in terms of a perturbative expansion in the angle between the beams and the colinear axis. We also numerically estimate higher order coefficients which cover arbitrarily large angles and thus any experimental configuration.