Simple recipes for separating excited-state absorption and cascading signals by polarization-sensitive measurements

The dependence of four-wave mixing and six-wave mixing signals on the polarization of the laser pulses is analyzed. Assuming that the dipole moments of the electronic transitions are not all parallel, we show that the excited-state absorption signal can be separated from the total pump-probe signal by two measurements with different polarizations of the pump and probe pulses. We show, furthermore, that cascading (third-order) signals can be separated from the fifth-order signal by two polarization-sensitive six-wave mixing measurements. We provide simple explicit formulas that express the excited-state absorption and cascading contributions, respectively, in terms of polarization-sensitive signals.