As researchers begin to use laser pulses with increasing bandwidths, the potential for the phase-mismatch and directional-filter distortions in measured 2D spectra increases described by the David Jonas group in 2007.
These distortions would appear even if the laser noise were eliminated and if the alignment were perfect. These distortions can cause artificially narrowed or square-shaped peaks. Adjusting the beam geometry and other properties of the spectrometer can lead to spectra with larger surface areas.
Here is a calculator for you to evaluate the phase-mismatch and directional-filter distortions in a BOX geometry 2D ES setup. The phase-mismatch is easily minimized by using a thin sample path length. The directional-filter distortion is more difficult to minimize. Jonas et al. state that both of these values should be <<1.
The bluest and reddest wavelength could represent the FWHM values of a Gaussian laser pulse, for example. The focal length applies to the curved mirror that focuses the beams into the sample. The total sample pathlength is the thickness of the sample or cuvette sample region, as long as the region of beam overlap is not thinner than this.