Precise phasing of 2D-electronic spectra in a fully non-collinear phase-matching geometry.

We report an experimental design for two-dimensional electronic spectroscopy (2D-ES) that avoids the need to measure notoriously weak pump-probe spectra. Retaining a fully non-collinear folded boxcar geometry, the described layout replaces pump-probe with heterodyned transient grating (het-TG). The absorptive component of the het-TG signal is measured directly, following a straightforward optimization routine. The use of het-TG achieves an improvement in signal to noise ratio by almost two orders of magnitude. As a result, 2D-ES-signals down to 0.5% can be clearly resolved.