Optical spectroscopy allows to study in a laboratory -  as opposed to inelastic neutron scattering or inelastic diffraction x-Ray that require large scale facilities - the excitations of matter such as phonons, magnons, interband transitions as well as the characteristic gap of superconductivity or charge/spin density waves. The advantage compared to angle-resolved photoemission (ARPES) and scanning tunneling spectroscopy (STS) relies on the fact that it is a bulk probe, being less sensitive to the surface state (actually the penetration depth varies with the incident photon energy because of the different excitations encountered). Compared to inelastic neutron scattering, that is also a bulk probe, the needed sample volume is smaller. Indeed, for this technique only the sample area is relevant and imposes a cut-off at low energy because of the diffraction limit.

  1.     STAKES

  2.     PRINCIPLE

  3.     THE VERTEX