 Polarized light in one direction only gives access to some Raman–active modes, but rotating the polarization gives access to other modes.Each mode is separated according to its symmetry.The symmetry of a vibrational mode is deduced from the depolarization ratio ρ, which is the ratio of the Raman scattering with polarization orthogonal to the incident laser and the Raman scattering with the same polarization as the incident laser