Figure 2.

Schematic depiction of a vibrational SFG experiment with the psp polarization setting, where p indicates polarization on the plane of incidence (the xz plane) and s indicates polarization perpendicular to that plane (i.e., along y). The polarization is specified in the order of sum frequency (detector), visible, and infrared. The psp polarization setting isolates four elements of the second order susceptibility tensor (χ⁽²⁾). Among these four elements, ${\chi }_{xyx}^{(2)},{\chi }_{zyz}^{(2)}=0$ due to the C_∞ symmetry of a non-centrosymmetric interface (xy-plane) about the z-axis and ${\chi }_{xyz}^{(2)}=0$ given the symmetry of the Raman polarizability tensor in the absence of electronic resonance. Ignoring Fresnel factors, the chiral response is given by ${\chi }_{psp}^{(2)}\propto {\chi }_{zyx}^{(2)}$.