Separation of cascaded and direct fifth-order Raman signals using phase-sensitive intrinsic heterodyne detection

Cascaded third-order Raman signals can be separated from direct two-dimensional fifth-order Raman signals using heterodyne detection with a local oscillator that is cycled from in-phase to out-of-phase with the direct signal. The difference of these scans gives the direct signal, while the sum gives the in-quadrature cascaded signal.