  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.
