Coherent multidimensional spectroscopy (CMDS) is a powerful nonlinear optical technique, which is used to study femtosecond dynamics in broad range of systems. The information obtained in CMDS experiments is spread over multiple dimensions. In most common CMDS technique called two-dimensional (2D) spectroscopy signals are resolved on two frequency dimensions. Mapping over several dimensions allows for unravelling correlations between different optical transitions and therefore obtaining information on couplings in the studied system. Accordingly, CMDS techniques allows for determining molecular or material functions with unprecedented details.

CMDS uses sequences of short laser pulses with varying delays (and phases) to excite the sample, after which either photon-echo-type signal or incoherent “action” signal is detected. The latter can be, for example, fluorescence, photocurrent, photoelectrons or any other signal which can appear as a result of interaction of the laser pulses with the studied system. The photon-echo-type 2D spectroscopy makes use of geometrical arrangement of the laser beams and phase matching effect for coherent signal generation and subsequent detection.

CMDS techniques can be combined with variety of microscopes or scanning devised to provide not only time, but also spatial resolution, which is especially useful in studies of nanostructures and functional morphology of the materials.