One of the ways to experimentally determine ω ω TO and ω ω LO is through Raman spectroscopy. As previously mentioned, the phonon frequencies used in the LST relation are those corresponding to the TO and LO branches evaluated at the gamma-point ( k = 0 ) of the Brillouin zone. This is also the point where the photon-phonon coupling most often occurs for the Stokes shift measured in Raman. Hence two peaks will be present in the Raman spectrum, each corresponding to the TO and LO phonon frequency.